Actually, that is only a decision you can make. You need to check out the GSM lineup and then compare them see which fits you needs. They all will handle calls and a few apps and all will do email, Facebook, web IF you have a BB data plan.
Read this from the FAQ:
Buying a BlackBerry off eBay - BlackBerryFAQ
It has good to know information for buying any used BB whether from eBay or from any other source.