Try them both. They aren't that similar at all. In my opinion, keep salsa, but that's because I hated Mimi. It'll depend on what kind of stimulation you like more. If you like pin pointed...salsa you will love more than Mimi. If you like broad vibrations...Mimi you will love. They are totally different in my opinion.
Should you not like one...sell it on the classifieds. There are always people willing to pick them (Mimi, Salsa, etc) up because they are favorites. However, if you are wanting actual cash for it... don't list them at a high cost. No one is going to pay full price or even 40% off the price for a used toy. If you sell a $80-$90 item for $20-30 dollars it will sell fast.