The main issue I had with the stock version of SwiftDroid - and this is based on 1.6, I think - was that it oversized the screen resolution, making various widgets and even text look bloated and slightly distorted. There may have been a fix for this somewhere, but I was never able to find it. Also, initially MMXTREM had some nice bug fixes (like the battery indicator) and seemed to run more smoothly on my GT540. In fact, it still does.
I would really lije to maintain a collection of various ROMs to test them and play them off one another. They're all really great work, and I appreciate the effort the developers make to release them to the GT540 community. Sadly, my SD card won't let me make a direct backup (it always throws a write error, even in recovery), so I have to stick with just one. I wish there were a way to do a clockwordmod type backup, but push it to my laptop through USB. For now, though, I work with a single ROM, and so far MMXTREM has been worth the commitment,