but do Chipmixer participants have more merits? Yes, (96% are merit sources, so getting some is simple), but I can't say the same for Bestchange participants.

Wow, I almost fell out of my chair when I read this. 96% of CM participants are merits sources ?? I'll have to check that.
So of the 55 participants of the CM campaign, 28 (5 of which are Staff members) are indeed merits sources.
Of the 25 participants in the Bestchange campaign, 6 are merits sources.
You can deduce what you want from these numbers, but you have to take into consideration that the CM campaign is 137 weeks longer than the Bestchange campaign. Probably a small insignificant detail.