There is really no way of knowing, but based on what we've seen so far, you are better off farming the most useless, most expensive to gear and rarely used character on your roster.
Case in point - Dengar. Rarely used - check. Expensive to gear - check. Useless - very situational - check too. So CG brought R2 into the Chewie event just to make Dengar's unique highly useful, although by all accounts Lobot should have been there instead. Most people didn't have him geared, so panic farming ensued == profit.
TL;DR - I recommend either Gamorrean Guard or Tusken Raider.