I have both a Lumia 920 and a Z30. They are both great devices. BB10 is super smooth (like WP 8 and 8.1) but it does require a little more in the memory department. Camera is better on the 920, email is slightly better on BB10 (the Hub is very good indeed). Notifications are handled a bit differently on both platforms and I give the nod to BB on that one; battery is better on the Z30 (it is bigger), however I routinely get a full day with the 920 on a charge. As for the interface - WP hands down as I really prefer the overall experience. All my opinions - I routinely switch between the two for a daily driver, and am comfortable with either one. Really want to see BBM on windows phone soon though.