bPermissions is apparently easier to set up. I don't believe it but that's what most people think. I would personally say PermissionsEx is "better" because once you get into more detailed/complicated stuff, Pex is a lot easier/simpler to understand.
I say that bPermissions is easier to understand and set-up. If you want no hassle with setting up your server perms and quick and easy rank management, you should use bPermissions. If you want to push your plugins out to extreme, then I suggest you should use PermissionsEx. In those cases, it is way easier to use. With bPermissions, you will be struggling.
I'd say PermissionsEX is by far the easiest and best one out there (in my opinion). It's incredibly simple (to me at least) and has worked for me 90% of the time. The other 10% was because I messed up something. I've personally used both bPermissions and PEX; PEX is much 'faster', cleaner, and simpler to use. It even has in-game commands for ranking up (i don't know is bPermissions has added that yet or not).
I've used both and I prefer PermissionsEx over bPermissions. I suggest you try both of them out and see which you like better as they are both fantastic permissions plugins
was just asking because i have set up bpermissions and when i set peoples groups in game it doesn't move them to their group :S and then when i look at permissionsex i just get overwhelmed.. sucks trying to setup a server on your own
Basically, I'd say go with PermissionsEX.