Have you ever used the straight up cm10? How does viper compare? I am tempted to try viper tonight
CM is lighter weight. Runs a little quicker, but is more utilitarian. You can do a zillion themes with it, but it is not quite to the extent of theming you can get with Viper. The 4.2 GAPPS camera, if it worked perfectly, would still be not as good as Sense... but it is much closer than pre 4.2 camera was. Even with the multitasking tweaked on viper, that still runs better on CM (you can read an html book, and it will keep your space, whereas Sense will reload and lose your place for example). In general, when comparing Viper to the latest 10.1 release the other day, Viper runs a bit more reliably, with better battery and better camera. Fewer issues overall, but then CM 10.1 is still unofficial.
I think Viper is the one to have for your stable base, once you get that setup with a nice backup, try the others out there for a day or three and see what remains on your issue list. Viper is my "safe haven" right now, but I am running CM at the moment.