I vote for 2 different batiks in a block paired with solid black. (Batiks often look great with a warm color like solid beige. Another idea is to pair them with any shade of a solid color, perhaps blue.) With 2 different batiks per block, if you sew 6 sets you might get 72 different batiks to put in a quilt top! It would be lovely!! On the other hand, if you sew 2 sets and the swap was for 1 batik per block, you might get 12 batiks (or less). If I sewed 2 sets I'd rather swap to get 24 batiks than 12...