Dice chips are a given, so here are a few of my thoughts on the rest:
1. I'm slowly warming up to a few ceramics, but I don't think I'll ever really like slippery, worn-out casino Chipcos. And I've lost most of my enthusiasm for China clays, although the newer chips are probably much better than the older ones.
2. Any face art that looks cartoonish (typically on ceramics). Those remind me of kids' toys, not for use by grown-ups. (I know, chips are supposed to be fun. After a few drinks, I would probably be OK with this one... but I'm not supposed to drink anymore.)

3. Inlays that use text over pictures, or have small denoms. Makes things too hard to read.
I can live with giant inlays and hotstamps, Paulson home sets and Bud Jones chips, coin-in-centers and Claysmiths, tri-moon spots and fantasy casinos. I actually liked the CDIs. But you can keep the Flamin' Hot Doritos.
As far as colors and spots go, it seems to me that when casinos swing for the fences, they often get one really nice chip and one awful one in the set. So it would be easier for me to pick individual chips that I don't like, instead of entire sets. IMHO: the Treasure Casino $5 reminded me of a pizza, and the Isle of Capri $5 was almost the same. I think the Crystal Park bumblebee $5 is the low point of a bold set. And the Jack Cincinnati $100 primary chips (brown and green spots) are pretty ugly, especially compared to the secondary $100. But YMMV.