Most of these packages should give you a trial period of some sort. I would recommend managing a single customer’s relationship history in each of the systems and see which you and your sales force like most.
Do remember that any CRM system brings some formality to the sales process, and that may be meet with resistance by your reps if they are used to doing everything on the proverbial “back of napkin.” There will always be a balance between whether the system is more management or sales friendly. If there are lots of nice management reports, there are also more data entry requirements on sales that will likely frustrate them. Striking the balance that is right for your company, or changing comp plans to support use of the system are key here.