I personally have not used the Nexus, but I've used the Infuse (for about a year) and then switched to an SII (at&t). For me, the difference was night and day, as far as not having to deal with bugs, random freezes, reboots, etc. A lot of people who never really used both phones kept saying that the Infuse is just as good as the SII, but after having used both for a significant length of time, I find that statement rather misleading.
I would definitely say the Nexus is the better choice. Plus, you'll have vanilla Android, so you will be first in line for official updates from Google (I'm assuming you're buying the unlocked version from the Play Store). The Infuse has already been abandoned by Samsung and at&t (its latest Gingerbread update was pretty awful - it was left unfinished, with little tidbits here and there missing, along with having issues). Obviously, the Infuse is not going to receive Ice Cream Sandwich.
On the Nexus, you'll already be on ICS and will receive Jellybean when it gets released by Google later this year.
With that said, there are a few points where the Infuse triumphs the Nexus:
-Super AMOLED Plus (the "Plus" means no pentile matrix, which is what's used on the Nexus; despite the Nexus having HD resolution on its screen, due to the pentile matrix technology, some people complain that it's a bit more grainy - however, I think this is kind of a moot argument, since with the Infuse's low pixel density, you can still make out pixels... so, it's kind of like, do you want non-pentile but lower resolution, or higher HD resolution but pentile; also, from firsthand reports, the Nexus' screen is stunning).
-8 MP camera (the Nexus has a 5 MP camera; a lot of people will say though that the MP count is not as important as it seems; still, I have read people complaining that the Nexus' camera is not too great, despite the better software features for the camera app).
-TouchWiz (pro or con, depending on whether you love/hate TouchWiz; this is Samsung's custom skin on Android; some people hate it, some people love it).
-Expandable Storage (the Infuse can have an external SD card inserted for addition of memory; I bought a 32 GB one and so I had 16 GB (internal storage) + 32 GB; the Nexus doesn't have this, so you're stuck at 16 GB; however, if you stream your music or just don't have a huge music collection, this once again is not a big deal; for me, I have tons of HD music videos and a lot of music files on my phone, so it was important to me).
Ok... Now with all that said, the Galaxy SIII is looming on the horizon for its stateside release. Unlike with the SII when they had that ridiculous half a year wait, this time, the SIII is supposedly launching in the U.S. during this summer, so that could mean anywhere between June, July, or August.
While the user experience difference from Galaxy SII to SIII might not be big enough to make me want to upgrade, I say this because the difference from Infuse to SIII would be monumental. Even between the SII and the Infuse, I got a much better user experience, so I can only imagine how big the gap will be for Infuse and SIII. If you don't need to purchase your phone right away, it might also be a good option to wait until the SIII gets released.
