[Crazy Jetty]

For me, this is a loaded question.
Grant Morrison fucked them both up, as far as I'm concerned.
I always had the most monumental crush on Jean.
However, the personal character growth Emma received as headmistress for Generation X put her on the map for me.

Then when Morrison got ahold of them, he pretty much outright ignored everything she ever did for Gen X, and reduced her to the untrustable villainous-turned-hero, who everyone doubted at every single turn.
And at the same time, they pretty much ran Jean into the dirt for me. I mean, they killed and resurrected her what, five times in one story? They literally took every single thing I loved about her and made her so rediculous I stopped caring altogether.

I also couldn't stand the whole diamond thing. I have no issues with changing, but when Morrison took over, he made so many changes that made no sense, and had no point. Just to mess with the status quo.
Basically... I don't really like either of them anymore. I didn't like Emma stealing Scott (But not because I'm a diehard Scott/Jean shipper. I really didn't like them as a couple, either. But at least they were a better match than Jean/Logan that seems so popular).
Basically... the only good thing that came out of Morrison's run as far as I'm concerned, was turning Xavier's back into an actual school for mutants, again.

To answer the original thread questions though...
Jean is established as being canonically the second most powerful telepath on earth. And when I was reading, Xavier suspected she was actually more powerful than he.
There's no way Emma could ever hold a candle against her in terms of power. That's pure canon.
Character developement, Emma had so much further to come, and indeed redeemed herself completely. Jean never had such an opportunity (Discounting the crimes of the Pheonix, which wasn't actually her.). So Emma has had more opportunities for personal growth and character developement. Jean stayed fairly stagnant, and unfortunately tied to the Pheonix, which hurt her severely for character growth.

As for Psylocke... man, she's so screwed up I don't think I could ever care about her. I liked her better before the whole body switch thing. That kills her for me. (Which says a lot, since I never found out about her until well after that happened)