I make a living out of 68HC11 (embedded firmware) for ~10 years and using 8051 for my hobby projects.
I'm using 8051 for three reasons
1) Avaiablity (in Malaysia)
2) Reasonable price for small quantity. Thanks to the second sources.
3) To aviod been accused stealing employer IPs.

Which one is more powerful? Standard answer : Depend..
Both have strength and weakness. It is up to application(and desinger) to utilize the best of it.

Thanks