The reason the S2 wins is because it has options. With iOS you have none, its the way it is out of the box or nothing. This might be fine for many, but for me i hate that i cant set the device up the way i like. For me Apple devices are impersonal, almost like they are not even my device, more like they are rented from Apple (and that's certainly how Apple treat you). If you dont like TW, get rid of it. You can even remove it from the ROM if you chose to.
The iPhone isnt about specs, but even if they were the new 4S loses for the most part to the GS2. The CPU is slower. A5 is no match for Exynos. The GPU element is fast though, probably faster in many ways, BUT the Mali-400 in the GS2 is more than capable enough and has better multimedia options, if slightly lower frame rates in some games (its locked to 60 anyway, which it usually maxes out games at).
The camera in the 4S is a big upgrade, but there is little reason to suspect that it will be much better than the excellent camera in the GS2.
The iP4 screen is something i take issue with. High resolution is nice, but its too small and the wrong shape. It letterboxes movies (or worse, crops them), making the image either distorted, reduced, or really small.
With regard to the Nexus Prime, its specs arent that much over the GS2. I see no reason to suspect that the Ti OMAP CPU is faster than Exynos. The GPU is still to be determined. It may have the same one as the iP4S, in which case it will be faster, but will it suffer the same limitations in its multimedia playback? Maybe its an iOS issue. The screen however is better, and is making me think about swapping my GS2.