Since the Evo 3d came out, there have been 4 updates for it already, I'd say they are on the ball. Most new apps that only work on some phones work with the Evo 3d as well, such as Skype and Netflix. The GS2 is a benchmark killer, but if you read reviews of some of the newer games, like Reckless Getaway, you will hear all the GS2 owners complaining about the frequent crashes for that game, runs great on the Evo 3d. It's because of how the Mali 400 GPU in the GS2 handles texture compression if I am not mistaken. Yeah the benchmarks are great, but in overall every day use, you will hardly see the difference in performance between the two.
HTC Sense is also much prettier and in my eyes more functional than Touchwhiz 4. HTC is doing a good job giving us new widgets and themes to play with as well.
Lastly, you can debate about which screen is better. Nothing beats the GS2 right now as far as blackness level and eye popping color goes, however, it's still running at 800 x 480 while the Evo 3d is running at the future standard resolution, qHD.
More compatibility, better support by the manufacturer, easy to customize, nicer UI, and comparable performance when you look past the benchmarks, and the winner is clear.
There have been a lot of discussions and comparisons between these two phones, check this forum and maybe YouTube for some head to head comparisons between the Evo 3d and the european version of the GS2.
Lucky for you, all the major new phones for Sprint are going to be out in the next two months, so if you're in not too much of a hurry, you get to do some hands on time with all four candidates: Evo 3d, Photon, GS2, iPhone 5. It's a good time to be on Sprint!
Notice also that I didn't even mention the 3d part of the Evo 3d, to me it's just extra gravy and a conversation piece! Funny how girls always say "take a pic of me, I want to see what my ( . ) ( . ) look like in 3d!! Yes...it's happened to me! ;-)