I'm pretty sure you've asked this same thing years ago lol.

My answer still stays. Uniques summons like Diabolos, Eden, Quetzalcoatl, Cerberus, Ark, Fenrir and Anima are my favorites. Cerberus only design-wise, as what he does is pretty useless to me.

I do like some others, obviously, but I tend to like the unique and less common ones more.

Zalera is probably my favorite Esper from FFXII, even though they're very useless in my version (I also like Chaos, especially because that's the Taurus one, my Zodiac sign!).

I also really like Odin, namely the FFVIII one. And Shiva, because ice; favorite design..... Probably the FFXIII or FFXV one right now.

If I had to name ONLY ONE, I'd say Anima.

You're right. I couldn't remember if I made the post or just thought about it before.