Synergy is also a frankenstein sense rom like MikG. It's based off of the evo, evo shift, desire hd, and kingdom. Mostly Sense 2.1 with Sense 3.0
I haven't been on MikG since v1.01 so I can't really tell you the differences between the two at this point. But back then, they were very similar. Synergy does have it's own updater app that also has support for addons and themes which is a little fancy. Other than that, I'd say maybe just make a nandroid backup of what you got now and take Synergy for a spin for a few hours and see if you like it.
Truthfully, I'd say Synergy and MikG will be the most popular sense roms for the evo. Unless Calkulin (EViO) and flipzmode (Fresh) decide to do something new. At this point, the two roms are extremely similar.. the next thing to look forward to would probably be a perfect port of the carousel rosie from sense 3.0 and of course, kernels when htc releases the source.