For briars I prefer slightly bent, a wee bit more bent, really bent and fully bent. Pretty much any conservative bowl shape as long as the pipe is balanced and in a proportion I find agreeable.
Is there really a pipe that can compete with the classic Billiard? I prefer the straight, but own a few bent billiards. They are the classic everyone thinks of when you say "pipe."
Here are my top 4, and most of my collection consists of these.
Dublin, Apple, Rhodesian and Billiards(Lovat).
I am real traditional when it comes to my pipe shapes. I just believe a pipe should look like a pipe and not some type of animal or fish. The only other shapes I own are Brandy(3), Calabash(1), Cherrywood(1), Poker(1) and Zulu(1). I go for straight and bent but only 1/8 to 1/4 bent. I would be willing to bet most people think I have a boring collection of pipes as I have no pipes that are not a traditional shape.
Pot
Those are my top four. But there are too many great bulldogs, rhodesians, authors, eggs, diplomats, apples, zulus, churchwardens, freehands, etc. to just limit yourself to four!