If we knew what you required in a handset, then it would be easier to help. Be specific.
The only thing I am unsure of is whether or not the Bold 9650 will be eligible to also upgrade to BB OS 6.0, like the Curve 3G will be in 2011. If that doesn't matter to you, then it's probably a wash since they both have the same amount of built in app memory and share processors (I believe).
If you require any sort of decent web browsing, then I would steer you towards another device/OS, since BB web browser is arguably the worst of the heap. Really crappy UI and experience overall, for a smartphone. If you only need email/text/calls you should be fine though.
My company is swithching providers from AT&T to Sprint and we've been given the choice between choosing the BB Bold 9650 or the BB Curve 3G. I currently have a BB Curve 8520 and find that it meets my needs quite well. Is there any major advantage between the two choices we've been given?