Hey ashez... Doesn't Starmie totally stand out as the best one out of those three you mentioned? It has better speed and spA than Tentacruel (80 Base SpA isn't very high). Starmie can learn Grass Knot which is arguably better than Tentacruel's Giga Drain. The only thing Tentacruel has going for him really is better Sp Def and Bug resist for Abomasnow (which Heatran can do pretty well with). Kingdra without rain probably isn't worth it imo. As far as mixed attackers go, I think your best best are Sheer Force Nidoking and Dragonite, but yah, that's where I was saying... you might as well go all special or all physical since both of them learn TBolt + Blizzard. Out of the things you mentioned, I think you should go with Starmie because your team will appreciate the speed.