Thymeleaf and Spring are a very nice match. The spring integration of Thymeleaf is done as it's supposed to be and it was nicely documented how to get started.
I use this combination since one year in several projects and I'm still happy with the choice I've made at the time.
Thymeleaf propagates the so called "Natural templating", which means that the templates can be viewed without the template engine, they are html files with additional tag attributes which browsers just ignore.
This means that a webdesigner can design the page, hand it over to the developer and get back again if changes to the layout have to be made.
While I liked this idea a lot in the beginning, I soon realized that, as developers, we tend to create components to be reused. This results often in templates having either not alot to display or also an extreme amount of elements.
Imagine some switch statement in a table cell component which renders either checkbox, textfield, select box, and so on. The table template including this cell fragment does not resolve it without an engine. Or imagine the header fragment with all the style and js declarations. Css will not be available in plain file mode.
But you can add additional html tags and remove them during processing. So natural templating is still possible. Just a lot to write :)
There are support extensions around solving this issues (using JS to pull in the fragments for example) but I havent used them as my applications are normally deployed within 30sec and I'm even able to change the templates on the fly without a redeploy.
After you also have a quite nice eco system around thymeleaf. The ability to extend Thymeleaf is done in a way I really enjoy! (Having written two smaller extensions myself).
I prefer the layout dialect instead of the include approach. That's a matter of taste i would say.
Choosing Thymeleaf over Plain JSP is clearly favorable from my point of view. Take a look at the webpage and decide for yourself ;)