Chris as far as avoiding, in general you do not want ARC radios. Of course, if you get a good deal on an airplane with ARC radios, you can do slide in replacements from Mitchell or Narco, so I wouldn't pass up an airplane purely based on it having an ARC radio or two.
If you stick with Bendix King, Narco, Mitchell, Icom you should be fine. Much depends on age though, an older King radio may be useable, but not very desirable. Same is true of discontinued brands, or budget brands such as VAL. Best bet, if in doubt, do a google search on the radio in question, if it is a current model still in production, you should be fine, if not, you can always ask a specific question here. Incidentally, your questions on avionics will probably get a better response if you post to the avionics topic.
