TouchWiz 4 is amazing. No lag at all. The Exynos processor is very smooth and responsive and the screen looks great, colors pop. The icons are essentially the same (if that's what's holding you back from buying the phone that's weird). Plus, the GS3 is coming out soon which will be better than the One series.
----------
Not necessarily true. I, for example, like my GS2 and plan on getting the GS3 and not switching back to the iPhone which is nothing more than a trendy device. Apple did say to "think different".
Samsung Galaxy S3 should be the best phone of the year but after watching sense 4 videos and reviews on youtube, it won't matter much to take a step down and go with HTC phones rather than Samsung. It's more touchwiz than samsung, there is the option of rooting android phones and putting stock ICS but I have no experience with rooting, sticking with a good sense 4 android overlay is sufficient for me.