I own a Z10 and a 1520, so I can at least have something relatively similar. Here's my breakdown (they are, however, opinions, mostly)
Multitasking: BB (although it uses a lot more battery than WP)
Keyboard: WP
Consumer-focused functionality: WP
Enterprise-focused functionality: BB (although since MS is an enterprise company, I suspect they'll add the enterprise stuff before BB adds consumer)
Email: BB (by a hair, although I'll admit that I don't email a lot)
Ease of use: WP
hardware quality: WP
"palmability" (ease of use to hold in hands): Compared to the 1520, probably BB, but the 930 will be the same size, so that'll be a tie.