Three-strand nylon. Springs the length of the boat, bow and stern lines 2/3 length of the boat as a minimum.
1/2" is enough for your boat but 5/8" will give better 'hand'. I'd pick 1/2" because it takes less stowage space, important on a small boat.
Three-strand nylon has good abrasion resistance and tends not to snag. I wouldn't use braid for dock lines because it has limited stretch and is difficult to splice. Can't see the point in using expensive braid and then having to put snubbers in the line to create stretch.