Definitely like preassigned roles better! I feel like it fleshes out the characters more. Although I don't mind at all if there's room for customisation, but with an easily distinguishable (i.e. not just "X's magic stat is slightly higher so they're a mage type") base.

One system I'm very fond of is Baldur's Gate's, where you can tailor your main as much as you wish, and can then recruit whoever you like along the road, who are set character types, but still with some room to shape them yourself.