Grey has it all. Sorceress is great, witch is strong, ghost is straight up OP. Fortuna, shadowbat and jellyfish are quite good crafts, and you also get all the best destruction toys and get them early.
Red looks good on paper and in early game, but really is the worst later on. Metallo and scarab don't scale into late game, Moloch < Syn, bio suits and savior outfits I don't find that useful, one is useful to only get hit with no actual accuracy to fight back properly, the other is useless to those who don't get hit. Blood ax is nice on syns for those 5-6 per turn chainkills technically, but you actually can kill as much with electro-sword.
Gold is meh, same as grey but actually less stuff. Only useful in early game with it's 3 space suits and bravery boosting outfit for use with bravery-scaling weapons. Magical Girl is not that good, illusion equipment can do the same, but better.
Green... I don't even know the purpose of it. It's like the combination of what other codexes have, but less. Haven't tried Pestulator, though, it can be useful if it does not have the penalties of bio suit.