They are rather different from each other. Powers is a more traditional comic book, in that it features Superpowers and places a greater emphasis on continuity. The art is better in Powers also, the dialogue is undiluted Bendis (which I happen to like but YMMV). Q&E is naturally more realistic, and this tone is reflected in the styles of the art and the script.
Both are well worth a read, so it probably comes down to which you'd prefer, a spy thriller or a cop show set in a Marvelish Universe. My advice go with Q&E if you're looking for something a little different, and it has that rare thing in comics, a well written female lead.