Figured I'd weigh in on this as I'm taking a serious look at the Nexus, RAZR, and Rezound. Sense vs. Vanilla is obvious, IMO. Sense > Vanilla in terms of out of box experience through GB. ICS is unknown until released. If you like Sense, then the Rezound should be a the top of your list. If you prefer vanilla, then the Nexus should be further up with the stipulation that it is easier to get a Sense phone to emulate vanilla than it is to get a vanilla phone to emulate Sense. But, I'm a hardware guy, not a software guy, so here goes.
CPU: Nexus uses a dual-core Cortex A9 clocked at 1.2ghz, while the Rezound uses a dual-core Scorpion at 1.5ghz. I'm a huge fan of Dhrystone MIPS (DMIPS) as a measurement of a CPU's potential power as the numbers are consistent and predictable. Outside of this, any benchmark can be tailored to make one CPU look superior to the other and vice versa. With DMIPS taken into account, the Rezound wins 6,300 to 6,000. This is a difference of 5%, which is negligible at that point, IMO. (DMIPS numbers are rated 2.1DMIPS per clock cycle for Scorpion, and 2.5 DMIPS per clock cycle on A9). If history is any indication, A9 @ 1.2ghz should offer better battery life than Scorpion @ 1.5ghz, and the Rezound is rumored to have a smaller battery to boot.
GPU: Adreno 220 vs. PowerVR SGX540.
AnandTech - Samsung Galaxy S 2 (International) Review - The Best, Redefined
The Adreno 220 was designed to eliminate the edge that the SGX540 held over the 200 and 205. I didn't like that line of thinking as Qualcomm basically stated that they expected PowerVR to stay stagnant. While Android didn't get the new 543, the 540 was nearly double-clocked offering a significant performance improvement. So, did Qualcomm outpace PowerVR, or did PowerVR stay ahead? Let's look at the benchmarks from the above link. Where possible, benchmarks are done at 720p to give consistency with results rather than base the results on a device's native resolution. Since our target devices are 720p, this is actually very useful for us.
The triangle-throughput tests (geometric performance) shows a roughly 50% performance edge for the SGX540. That's HUGE. However, these synthetic tests use more triangles than any game out today or within the next year, so don't let this be a killer. I mean, the Mali400 was slaughtered on this test and we know that's an excellent GPU. Fill-rate tests show a different result, with the SGX540 holding a 100%-125% increase over the Adreno 220, which is essentially a bloodbath. It's clear that while Qualcomm did a reasonable job of beating out the old SGX540, the new one is just too much to handle. 540 wins, hands down. Also, keep in mind that these banchmarks were done with the 540 @ 300mhz. The Galaxy Nexus supposedly has it clocked at 384mhz for even more performance.
If you scroll down to the Rightmark tests, you can see comparisons done at device native resolutions (800x480 and 960x540). The Adreno 220 and PowerVR SGX540 trade blows with marginal victories here. That tells me that when there are smaller fill-rate and geometric requirements, neither GPU is taxed and the device becomes limited by CPU, memory, and/or refresh rate. But, at 720p, the SGX540 is the clear winner.
Conclusion: It is my personal opinion that the CPU in both devices is comparable. Your choice, slightly better performance (Rezound) or slightly better battery life (Nexus). This doesn't take into account SMP vs. aSMP, which we can debate for days and I don't think will make much of a difference this generation anyway. In terms of the GPU, the Nexus straight up slaughters the Rezound when you take into account a 720p display. The Adreno 220 is an awesome GPU, but the new SX540 is just "more awesomer!"
But, this issue is still "clear as mud." I'd vote Nexus for overall hardware, and software updates. I'd vote Rezound for style and Sense UI. Either would make a kick-ass choice.