I actually find myself liking the TouchWiz interface over HTC Sense. I've tried others HTC phones before and my SGS2 is the first android device I've owned. It's quite nice so I haven't bothered changing roms yet. I might if there's a significant battery usage improvement though.
I came from a Motorola Milestone/Droid which has a higher-res screen and the big font/menus of the S2 was a real turnoff for me first. I even thought about getting an HTC Sensation which has a slick UI with small fonts. But once I put MIUI on it I never looked back, the UI is just beautiful (a little iPhone-inspired though, but not copying the bad things - e.g. the 'back' button in the upper left corner). Don't think you will see battery improvements since the UI is mostly black-on-white as opposed to the default, which is suboptimal for AMOLEDs.
