I have three, no problems fitting a regular pipe cleaner through any of 'em. One note though, it is very easy to pack your tobacco too tight. Even with a tight pack it'll still draw easily so be careful.
When it comes to bowl sizes, the "classic" shapes (hyperbole, istanbul & Sniffer) are the largest. Algeirs, Dover, Genoa & Plymouth are your next biggest followed by the Apple, billiard, Dublin etc. Unless you find the bantam size bowls which are the smallest.
After I smoke a bowl I've taken to running hot water through the pipe to clean it. A wipe and a shake and its ready again. I've been doing this for several weeks now to no ill effect.