It really depends upon the brand.
Nominally my favourite is Salt and Vinegar but Golden Wonder's offering is like eating battery acid. Horrendous. If forced to eat Golden Wonder I'd go for ready salted or prawn cocktail. Walkers S&V are alright, but Kettle Chips and Mackies crisps S&V are both excellent, with the Kettle chips having the added advantage of leaving hundreds of cuts in the roof of your mouth to provide lots of surface area for the salt and vinegar to attack
Mackies are generally excellent, I'm partial to the haggis and pepper flavour, but scotch bonnet is also nice.
Non-potato answer: Roast Beef Monster Munch. I will absolutely die on this hill.