My favorite summon that appears in nearly every Final Fantasy is Bahamut. He is really powerful and ignores defense. A close second is Odin but that's mainly cause of his design. I wouldn't risk losing MP on him if he only has a chance of killing them. As for what game I liked summons in best? I would have to say VIII. The GFs were awesome in graphics and they had the most purpose. They didn't even require MP :q