III: Ifrit since it was the most useful even if you were using the lower tier Evoker Class.

IV: Leviathan or Asura because they are both super useful, and can be gained relatively early compared to Bahamut who is only really useful for two dungeons.

V: Golem is easily the most useful summon in this game. Syldra is a second choice since she'll carry you for most of the game until you acquire Levaithan and Bahamut.

VI: Alexander, first appearance and still my favorite incarnation. Love the quest you have to do to get it. Love it's attack animation. Love it's spell set. Great summon overall.

VII: Leviathan is easily one of my faves. Great animation, awesome power if you get it as early as possible, and it's water elemental nature makes it more useful than you would imagine.

VIII: Diablos is easily the most stylish and cool summon in this game. Hardly the most useful as a summon but it has a great Junctioning skill set. My second choice goes to Tonberry.

IX: Easily Bahamut, favorite design of his in the series. Fenrir is my secondary choice since I wasn't expecting to see himback as a summon.

X: Shiva is my favorite and the best redesign of the group. She's also super OP compared to all the previous summons and despite needing her limiter removed, I feel she's on par with Bahmut and all the advanced summons. Anima and Yojimbo are secondary choices.

XII: Zodiark, easily the best summon, especially in the vanilla version of the game since he had one of the easiest exploits to cause him to use his super attack. My secondary choice is either Belias for the Tactics nostalgia, or Chaos for the FFI nostalgia.

XIII: I didn't care for the summons in this game, but Hecatoncheir is easily the most useful when it comes to Adamantoise farming. Still hate the orgasm attack though...

XV: Shiva easily. Love the story elements with it and it's a pretty brutal looking attack. Always makes me smile when I see her or Leviathan instead of Titan and Ramuh who I see way too much of.

Tactics: Cyclops always stood out to me. Helps he's probably one of the stronger summons that doesn't take a bloody lifetime to actually cast without Short Charge.

Tactics Advance: Famfrit which is just a cool looking summon, is associated with my favorite race in the game, and is a tie in to Final Fantasy III no less.

Crisis Core: Odin got a nice touch up in this game.

Type-0: Bahamut Zero, even in NG+, I'm tempted to throw that boss fight just to see this awesome summon.