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For an example of plot option customization that I am still rather proud of please see:
How to change the default ColorData used in Mathematica's Plot?

For general customization I think you already outlined some good options. I personally favor the custom function method for maximum control. Another, perhaps cleaner method that I crudely copy from Leonid works well if you can pool options for all plot types in one list ($myoptions):

Update: changed withOptions to use the "injector pattern" so as not to disrupt functions if withOptions is used indiscriminately (withOptions[ 1 + 1 ]).

$myoptions = {Filling -> {1 -> {{2}, {Red, Purple}}}}; SetAttributes[withOptions, HoldFirst] withOptions[head_Symbol[body__]] := FilterRules[$myoptions, Options[head]] /. {opts___} :> head[body, opts] withOptions @ Plot[{Sin @ Log @ x, Cos[3 x]}, {x, 0, Pi}] 

Here I posted another method in answer to specifying plot ranges, but the method is very general and can be used for any options or parameters. It works by creating an UpValue assignment for the symbol given that applies to any head. This could of course be further restricted to apply to only one head or a list of heads. One could also include FilterRules as shown in the code above, depending on the effect desired. For example:

SetAttributes[setOpts, HoldAllComplete] Quiet[ setOpts[s_Symbol, pat_: _, spec__?OptionQ] := s /: (h : pat)[pre__, s, post___] := FilterRules[{spec}, Options[h]] /. {opts___} :> h[pre, opts, post], Optional::"opdef" ] 

Now a single option as used above is assigned to op1:

setOpts[op1, Filling -> {1 -> {{2}, {Red, Purple}}}] 

And used in Plot:

 Plot[{Sin @ Log @ x, Cos[3 x]}, {x, 0, Pi}, op1] 

Alternatively the options can be restricted to a particular head or head pattern. Here a different set of options, also named op1, is defined only for ParametricPlot:

setOpts[op1, ParametricPlot, Frame -> True, PlotStyle -> Thick, Axes -> None, MeshShading -> {Red, Blue}, Mesh -> 15] ParametricPlot[{{2 Cos[t], 2 Sin[t]}, {2 Cos[t], Sin[t]}}, {t, 0, 2 Pi}, op1] 

Using op1 in Plot will still produce the result shown earlier.

You could also use Alternatives in the pattern, e.g: Plot | ListPlot | Histogram or more complication patterns with conditions, etc.

For an example of plot option customization that I am still rather proud of please see:
How to change the default ColorData used in Mathematica's Plot?

For general customization I think you already outlined some good options. I personally favor the custom function method for maximum control. Another, perhaps cleaner method that I crudely copy from Leonid works well if you can pool options for all plot types in one list ($myoptions):

Update: changed withOptions to use the "injector pattern" so as not to disrupt functions if withOptions is used indiscriminately (withOptions[ 1 + 1 ]).

$myoptions = {Filling -> {1 -> {{2}, {Red, Purple}}}}; SetAttributes[withOptions, HoldFirst] withOptions[head_Symbol[body__]] := FilterRules[$myoptions, Options[head]] /. {opts___} :> head[body, opts] withOptions @ Plot[{Sin @ Log @ x, Cos[3 x]}, {x, 0, Pi}] 

Here I posted another method in answer to specifying plot ranges, but the method is very general and can be used for any options or parameters. It works by creating an UpValue assignment for the symbol given that applies to any head. This could of course be further restricted to apply to only one head or a list of heads. One could also include FilterRules as shown in the code above, depending on the effect desired. For example:

SetAttributes[setOpts, HoldAllComplete] Quiet[ setOpts[s_Symbol, pat_: _, spec__?OptionQ] := s /: (h : pat)[pre__, s, post___] := FilterRules[{spec}, Options[h]] /. {opts___} :> h[pre, opts, post], Optional::"opdef" ] 

Now a single option as used above is assigned to op1:

setOpts[op1, Filling -> {1 -> {{2}, {Red, Purple}}}] 

And used in Plot:

 Plot[{Sin @ Log @ x, Cos[3 x]}, {x, 0, Pi}, op1] 

Alternatively the options can be restricted to a particular head or head pattern. Here a different set of options, also named op1, is defined only for ParametricPlot:

setOpts[op1, ParametricPlot, Frame -> True, PlotStyle -> Thick, Axes -> None, MeshShading -> {Red, Blue}, Mesh -> 15] ParametricPlot[{{2 Cos[t], 2 Sin[t]}, {2 Cos[t], Sin[t]}}, {t, 0, 2 Pi}, op1] 

Using op1 in Plot will still produce the result shown earlier.

You could also use Alternatives in the pattern, e.g: Plot | ListPlot | Histogram or more complication patterns with conditions, etc.

For an example of plot option customization that I am still rather proud of please see:
How to change the default ColorData used in Mathematica's Plot?

For general customization I think you already outlined some good options. I personally favor the custom function method for maximum control. Another, perhaps cleaner method that I crudely copy from Leonid works well if you can pool options for all plot types in one list ($myoptions):

Update: changed withOptions to use the "injector pattern" so as not to disrupt functions if withOptions is used indiscriminately (withOptions[ 1 + 1 ]).

$myoptions = {Filling -> {1 -> {{2}, {Red, Purple}}}}; SetAttributes[withOptions, HoldFirst] withOptions[head_Symbol[body__]] := FilterRules[$myoptions, Options[head]] /. {opts___} :> head[body, opts] withOptions @ Plot[{Sin@Log@x, Cos[3 x]}, {x, 0, Pi}] 

For an example of plot option customization that I am still rather proud of please see:
How to change the default ColorData used in Mathematica's Plot?

For general customization I think you already outlined some good options. I personally favor the custom function method for maximum control. Another, perhaps cleaner method that I crudely copy from Leonid works well if you can pool options for all plot types in one list ($myoptions):

Update: changed withOptions to use the "injector pattern" so as not to disrupt functions if withOptions is used indiscriminately (withOptions[ 1 + 1 ]).

$myoptions = {Filling -> {1 -> {{2}, {Red, Purple}}}}; SetAttributes[withOptions, HoldFirst] withOptions[head_Symbol[body__]] := FilterRules[$myoptions, Options[head]] /. {opts___} :> head[body, opts] withOptions @ Plot[{Sin @ Log @ x, Cos[3 x]}, {x, 0, Pi}] 

Here I posted another method in answer to specifying plot ranges, but the method is very general and can be used for any options or parameters. It works by creating an UpValue assignment for the symbol given that applies to any head. This could of course be further restricted to apply to only one head or a list of heads. One could also include FilterRules as shown in the code above, depending on the effect desired. For example:

SetAttributes[setOpts, HoldAllComplete] Quiet[ setOpts[s_Symbol, pat_: _, spec__?OptionQ] := s /: (h : pat)[pre__, s, post___] := FilterRules[{spec}, Options[h]] /. {opts___} :> h[pre, opts, post], Optional::"opdef" ] 

Now a single option as used above is assigned to op1:

setOpts[op1, Filling -> {1 -> {{2}, {Red, Purple}}}] 

And used in Plot:

 Plot[{Sin @ Log @ x, Cos[3 x]}, {x, 0, Pi}, op1] 

Alternatively the options can be restricted to a particular head or head pattern. Here a different set of options, also named op1, is defined only for ParametricPlot:

setOpts[op1, ParametricPlot, Frame -> True, PlotStyle -> Thick, Axes -> None, MeshShading -> {Red, Blue}, Mesh -> 15] ParametricPlot[{{2 Cos[t], 2 Sin[t]}, {2 Cos[t], Sin[t]}}, {t, 0, 2 Pi}, op1] 

Using op1 in Plot will still produce the result shown earlier.

You could also use Alternatives in the pattern, e.g: Plot | ListPlot | Histogram or more complication patterns with conditions, etc.

For an example of plot option customization that I am still rather proud of please see:
How to change the default ColorData used in Mathematica's Plot?

For general customization I think you already outlined some good options. I personally favor the custom function method for maximum control. Another, perhaps cleaner method that I crudely copy from Leonid works well if you can pool options for all plot types in one list ($myoptions):

Update: changed withOptions to use the "injector pattern" so as not to disrupt functions if withOptions is used indiscriminately (withOptions[ 1 + 1 ]).

$myoptions = {Filling -> {1 -> {{2}, {Red, Purple}}}}; SetAttributes[withOptions, HoldFirst] withOptions[head_Symbol[body__]] := FilterRules[$myoptions, Options[head]] /. {opts___} :> head[body, opts] withOptions @ Plot[{Sin@Log@x, Cos[3 x]}, {x, 0, Pi}] 

For an example of plot option customization that I am still rather proud of please see:
How to change the default ColorData used in Mathematica's Plot?

For general customization I think you already outlined some good options. I personally favor the custom function method for maximum control. Another, perhaps cleaner method that I crudely copy from Leonid works well if you can pool options for all plot types in one list ($myoptions):

Update: changed withOptions to use the "injector pattern" so as not to disrupt functions if withOptions is used indiscriminately (withOptions[ 1 + 1 ]).

$myoptions = {Filling -> {1 -> {{2}, {Red, Purple}}}}; SetAttributes[withOptions, HoldFirst] withOptions[head_Symbol[body__]] := FilterRules[$myoptions, Options[head]] /. {opts___} :> head[body, opts] withOptions @ Plot[{Sin@Log@x, Cos[3 x]}, {x, 0, Pi}]