My wife and I just switched to Sprint and got new phones. I got the Galaxy S2 and she got the Photon. We got the different phones because we were torn on the 2 and wanted to compare them, and then take advantage of exchanging them within 14 days if we needed to. We were originally looking at the EVO 3D and the iphone 4s too.
So far, the phones are very comparable. I think I might switch to the Photon though. Here is my review (btw, I am new to android and sprint, I had tmobile blackberries for a while).
Galaxy S2
Pros (when compared to Photon) - The camera is better. The screen is "prettier". It has a wow factor when people see it. The interface is a little better looking (ie, the clock, and icons just look cooler than the photon - but I think you can customize the photon).
Cons (when compared to Photon) - The screen colors are also a little "fake". Once the wow factor is gone, people poke fun at the huge screen and size (they call it a tablet or an ipad...ha). It feels cheap. It is uncomfortable to hold in your hand while talking, texting, and browsing.
I also put the phones side by side and did a few browser searches for various sites and the photon was faster every time. sometimes by only 1 or 2 seconds, but sometimes by about 10 seconds+.
Also, when we've been out and about, the photon shows up as having a few bars more than the G2 SOMEtimes...
So bottom line, the G2 is a cool looking, fast, awesome phone with a nice camera. The photon is a fast, cool looking phone with great reception and a durable build. The camera on the photon sucks (but you can quickly edit them to look okay). It really is a toss up on these phones, the G2 is cooler, the photon works a bit better, but they are very similar.
Based firstly on the way they feel in my hand, and then secondly on the reception/speed, I will likely be returning my G2 for the photon. If it wasn't for the G2 having a better camera, I already would have changed them out.
one last thing - they make an otterbox for the photon (best case for ME by far) and they do not for the Sprint G2....
I'll reply if I change them out and I will post pictures from both cameras to show you what I'm talking about......