Mama's is easily the best falafel and pita I've had outside of Israel. Not really a "restaurant," though - more of a falafel bar.
As for Yi-Tzi Peking, overall it's pretty good. The sushi is excellent. I also like to support them - the owner does not-well-publicized community service. For example, he gives meals to bikkur cholim and refuses to take money for them. My wife found that out from someone at bikkur cholim and commented to the owner, who apparently didn't want people to know about it. So, of course, I'm announcing...
What about Yi-Tzi Peking in Bala Cynwyd? I've seen good things written about it and intend to go there on a future visit to Philly. A previous comment spoke about the need for a reservation. Under the supervision of Community Kashrus of Philadelphia and the Star-K.
145 Montgomery Avenue
Bala Cynwyd PA
I hope this helps.