For a pump I'd suggest the good old Remington 870, if you're willing to spend up to $700, I'd get a really nice wingmaster not the lower grade express.
For an autoloader, I'd look into a Beretta 390 (if you can find one) or the 391. Excellent auto, extremely reliable been seeing more and more of them on the clay fields.
For trap, you want a long barrel, at least 30in, 32in would be better. A high rib and/or monte carlo stock would be helpful.
If you want a good all around barrel, good for skeet, trap or sporting, 28in would be ideal.
Suggestions are great but really go out and try some of these shotguns and see what fits you the best, that should really be the determining factor.
HTH
-Dan