These days, just pick something fun and play it. If you really have to pick the strongest out there.. probably psychic based mostly around Firk with some Jellebrium. If you want easy to forge (fewer legendaries) then I'd go for Adaptive Boghoppers. That's Tidemaster + Defiler + spell spam (e.g. Marsh Song, Darkmarsh Warsong, Cleansing Mist, Bubble of Protection etc.).
