I have an 8310 and maintain the 9000 for several people at work (figures I'd get the cheaper one - I'm just the IT guy
). If I had my choice I would get the 9000. I think google maps works better on the 9000 and it seems like the 9000 is faster in general. The screen is definitely better.
I have also messed with the Perl but hate the keyboard.
The 8310 has very good call quality (I'm with AT&T) and there are a lot of free things out there (ringtones, themes, etc). I like the ability to have a full mp3 for ringtone (I think this requires media card) and the Outlook contact sync. The BIS is very nice and it connects right to our non-Exchange email server with no issues. Almost every problem I have had with the phone went away once I started learning how to use it. Apps are all over the place and really enhance the BB experience.
I have unlimited data and 400 messages a month for about $35 - add taxes, fees, government crap...
I am not an expert, but I thought since I was new too, you would benefit from another newbie opinion.