Baker, because it just opens up a world of new possibilities for the opening, and anything with coin tokens is generally pretty cool.
Pretty much anything with +Action or +Buy, because engines are fun!
Tunnel, Rats, Hoard, and Gardens, because they aren't often the best strategy on the board, but it's fun trying to make them work anyway.
Black Market and Knights because I actually kinda like the random, silly elements they add.
KC, Goons, Grand Market, Wharf, and Bridge because they each can make for really satisfying megaturns.
Marauder because Spoils and Ruins are both pretty fun.
Necropolis because dang, +Action in my starting deck!
City because it can really change the dynamic of the game AND can turn into a one-card engine if you activate it.
Peddler because it's a cool idea and satisfying if you can exploit it.
Colony because it means more time to play with my engine.
University because I love +Action and I love free engine pieces.
....I am going to list 90% of the cards if I don't stop myself!