The U853 is a new version of the AT853. The U853 has better stats on paper and is RF shielded. The CMC-8 is similar to the 853's, but smaller in size. The CMC-8 is slightly bigger than the Core-Sounds, and the U853 is about 2-3 times bigger...
I prefer the U853 over the CMC-8(AT943), but if size is an issue, I would go with the 943s.
IMO, if you don't tape that much and you don't want to spend a whole lot, I would just buy the Church Audio preamp and cardiod mics. They sell as a cheap package. The sound of Church's mics is very compairable to the AT mics. The only reason I would pick the AT mics over the Church mics is the interchangable capsules.