I'm not going to tell you specifically who to use, but I can help give you an idea of what I think you might want.
You say that you are more of an offensive player - luckily for you, there are some defense-oriented Pokemon out there that can still do pretty impressive damage. One key factor with defense-oriented Pokemon is their typing - even with massive defensive stats, a Pokemon that has 6 weaknesses and only 2 resistances for example is going to be pretty poor at defending against attacks. Although a lot of resistances isn't necessary, since even a Pokemon that just takes neutral damage from the vast majority of types can be a very effective defender, it is a bonus.
Moving to specifics, Pokemon that are good at defending whilst still packing a decent whallop behind their attacks are usually the ones that can either power up their offensive stats whilst still keeping in line with their defensive role (Calm Mind/Bulk Up/Curse, or Charge Beam basically) or Pokemon that just happen to have a high offensive stat as well as decent defensive abilities. That way, you can take plenty of hits whilst still dishing out a decent amount of damage back.
Snorlax, Cresselia and Suicune all carry a means of boosting their main offensive stat as well as one of their defensive stats, with Snorlax carrying Curse and Cresselia/Suicune both having Calm Mind. Cresselia also can learn Charge Beam, which on a stall oriented Pokemon can prove to be deadly if the opponent can't force it to switch out. Regice is also a potent carrier of Charge Beam, and has quite high Sp.Attack to back it up as well.
Finally, examples of Pokemon that carry good defense and good offense are Snorlax (again,) Empoleon, Vaporeon, Swampert, Rhyperior, all five Rotom Appliance Formes and also the Milotic you already have.
