I used to think Freybug were lame. Now they're one of my favorite early demons- Hinder, Tormentor, and Swiftness, and all you have to do is play tag! All great skills for cowardly summoners like me who don't like melee.
In terms of what demon I basically always want if I'm serious about progressing- Jiang Shi. They're basically self sufficient right out of the box, and slapping the easy-to-get Gluttony and Flesheater on them just solidifies their unmatchable staying power. I wouldn't be at all surprised if they lost Leechbite in some future build, making you wait for Ilomba before attaining maximum HP-drain capacity. But then that would make Jiang Shi packs less threatening... so maybe not.
My old early favorite used to be Chindi- lots of resistances and some pretty flashy moves. They can be scary to fight but are actually quite reasonable to negotiate with despite all their howling, something it took me a long time to find out, because I was too scared to negotiate with them for a long time due to the 'serious consequences' the game warned me about...
My favorite Unique is still probably Miadchaion the Unspellable. What can really compare to a bunch of hooligans shouting their enemies to death? Though I'm suddenly curious, does Mute actually prevent the use of Mighty Roar, since it's a physical ability?
The demon that is inexplicably my #1 favorite is Acheri. They're mostly just little annoyances but I always think 'well MAYBE I could do something cool with all these powers.' And then I never do Their dialogue where you warn them that you're infected and they just go 'sick shmick, gimme the goods, slick' (I'm paraphrasing slightly) cracks me up too.
Favorite Summoner- Ludoc gets props for treating his demons like friends, but really, he should've been a Pokemon trainer instead. To be fair, I haven't seen the later summoners enough to completely remember their themes, though. Paracelsus the alchemy nerd, Lioth the lategame something, and what's his face the slavering madman.
Favorite Hero- though she's not too exciting and she usually kicks my ass and sends me running to the next floor in shame, that really just reinforces my headcanon of Madevra being the true hero of the tower. Clearly she and Ludoc should team up in a wacky buddy cop comedy. Zaji can guest star as the plucky comic relief and mascot.
What are your favorite things?