Always Lotad. Tangrowth also has VERY good physical defense and should be able to take at least 1 field boosted physical fire move if trained properly and then retaliate with ancient power. Cradily functions similar to Tangrowth just on the special side, although its SpD isn't as high as one would wish, but it does have access to Ancient Power+Brine naturally and other useful moves via TM/Breeding. Also any pokemon that learns Rain Dance in any way, off the top of my head Amoonguss, Roselia, and Gogoat all learn it by TM, with Budew learning water sport as well.