Trainers like Lillie and Acerola are always popular, especially in rare variants
Aetherize Since Aetherize doesnt care who the creatures it bounces are attacking, it works as a powerful political piece in Commander

Fabled Fire King Firewall Fishborg Flamvell Floowandereeze Flower Cardian Fluffal, Frightfur, Edge Imp Forbidden Fortune Lady Fossil Frog Fur Hire Fusion Fusion Monster G Gadget Gagaga Gaia the Fierce Knight Galaxy, Galaxy-Eyes Gate Guardian Geargia Gem-Knight Generaider Genex Ghostrick Ghoti Gimmick Puppet Gishki, Aquamirror Gladiator Beast Goblin g goblin rider tentative G Gogogo Gold Pride Golden Lord, Eldlich, Eldlixir Gorgonic Gouki Gravekeeper Guardian Guardragon Gunkan Suship Gusto H Harpie Hazy Flame h heart tentative H Hecatoncheires Herald Heraldic Beast HERO Heroic Challenger, Heroic Champion Hieratic Dragon, Hieratic Seal Holy confectioner tentative Horus tentative I Ice Barrier Icejade Igknight Impcantation Infernity Infernoid, Void Infinitrack Invoked Inzektor Iron Chain J Jinzo Junk Jurrac K Kaiju k kaimetu tentative K Karakuri Kashtira k kenran tentative K Killer Tune Koa'ki Meiru Kozmo Krawler Kuriboh L Labyrinth Wall Lady of Lament Laval Libromancer Lightray Lightsworn Link Monster Lunalight LV, Level Up

You can do some interesting things using effects like Sword of Hearth and Home and Bazaar Trader, the latter of which can give you a treasure for passing on something you already borrowed, and making sure it never goes back
That said, if your goal is simply winning as much as possible, the full ten Puppy version is currently putting up the better tournament results