I haven't been on coach on the Continental 73NGs yet, but First Class is excellent. The seats are more comfortable than their counterparts on the 733s and 735s.
I've done the MD80 on the EWR-BUF run many times too and its quick flight (usually 40-60 mins) so choice of seats isn't really a big deal. Try and get in the 2 section of the 5 across though.
As for the ERJ, the only decent seat is 1A, but that is held for Elite members as some kind of quasi first-class. If you cant swing that, then go for the bulkhead - i think its 2BC on the ERJ-135 and 3BC on the ERJ-145, but I'm not positive.
"The A340-300 may boast a long range, but the A340 is underpowered" -- Robert Milton, CEO - Air Canada