Personally I didn't care for the two APA conferences that I went to... too big and I wasn't all that impressed with the talks that I attended.
If you're interested in academia, think about the AAP meeting. It's smaller and is very heavily focused on academic practice. If you're interested in a general psychiatry conference, I liked the American College of Psychiatrists annual meeting - again, much smaller than APA and I thought the quality of the talks was much greater (though also much less variety). I also really liked the ACLP annual meeting... even if you're not interested in C/L, I think a lot of the content of the conference is very easily applicable to general psychiatric practice.