Cheese & onion, plain salted or salt & pepper.
Though I will eat most flavours except for the stupid hot spicy stuff. I eat crisps for pleasure, not for pain.
But really not a fan of salt & vinegar and pickled onion. Not because I don't like the flavour, but because they're just way over seasoned. Same applies to some varieties of Worcestershire sauce crisps - French Fries or ordinary Walkers are fine, Seabrooks shrivel your mouth dry after just a couple of bites. Not pleasant at all.
Oh yeah, and Tesco's "Finest" roast beef & horseradish. Don't eat them unless you are in a dire need of exploding your sinuses.