LogFAQs > #872661652

Here's probably the best things you can do:

-Yugi and Kaiba have good cards in the 20's - Fusion Substitutes. Always good to have those. Kaiba gets Lord of D as a drop as well.
-Mai has Windstorm of Equatia or whatever it's called in the 20's. Really damn good trap.
-Bandit Keith's skills are all really good, and he gets Metalmorph at I believe 23. Metalmorph is invaluable.
-I maxed Weevil and I have used nothing. He does get a skill that automatically puts between one and three Parasite Parasides in the opponent's deck (when they draw it they lose 1000 LP, weak monster auto-summoned to their side of the field, all of their monsters become insects).
-Rex sure does exist. He's pretty much set the instant you get Jurassic World.
-Mako has water cards. Honestly everything you can get as drops from him is better than what he can offer through leveling.
-Ishizu is bad until Necrovalley becomes a thing.
-Odion is probably the hardest but the most fun. His skills other than Chain Reaction are crap, but Serket is a monster's monster, Curse of Anubis is a damn good trap card. He can give you a fun gimmick deck and then Curse of Anubis is fun.
-Pegasus gets Toon Rollback in the early 20's, which makes a Toon Summoned Skull OTK beyond easy. Mimicat also exists for a Toon deck. He also gets Mind Scan, which is brutally good.