3" no question.
I have a 3" single and a 2" double (aka 'truck size'). The 3" is much more comfortable. Part of the difference is the foam. The 3" is soft foam and the 2" is hard foam.
"Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain