TOD: I like the think-cut brasserie-style fries that are really crunchy on the outside and soft at the center best, though Greek-style fries, a little meatier, are good. And, well, fries with truffle salt are irresistible. As long as they're not soggy, all fries are great.
As for onion rings, there's a place in town, Big Bob's Burgers, that adds a little caraway seed to the beer batter. The rings are thick cut and they're fried to a crunchy, deep brown, so they crackle when you bite into them. (They also know how to peel an onion, so you're not biting into something stringy that pulls out of the coating.)