If you are from N900, my instinct would be Z30 fits you better.

Z30 has big screen and decent ppi so browsing/reading/multimedia is a breeze.
BB10 UI will feel more similar to N900; multitask miles better than iPhone
BB10 keyboard feels great
Browser is fasssst

Some downsides are
- Poorer picture quality (especially in low light)
- Much much less apps/games
- Some Z30 seems to have stability issues?