Never been a fan of the old school, high stance/side arm poke-strokers of the past. But I guess during Mosconi's time such mechanics are considered the normal standard. The fact that they made it work baffles me.
Ismael Paez's stroke is one that I still remember as being particularly unaesthetic. He did very well at the 2000 World Championships, but ultimately his jumpy stroke was his undoing, losing in the finals to Chao Fong Pang with an embarrassing scoreline of 17-6.
In the world of snooker, you also have players with horrible cue actions. Alex Higgins is a true genius, but his overall mechanics reminds me of a low-level pool banger. Barry Pinches' set-up is all over the place--I dare you to find another current top snooker pro with a funnier way of approaching the shot.
I believe there are two main different reasons why some top players develop unorthodox technique which may seem "ugly" to most people. The first case is that the player started playing at an early age with the wrong technique and didn't have any proper coaching to get it fixed, until the stroke became "grooved", ie Efren, Bustamante. Another probable reason is that the player is constantly tinkering with his technique until it becomes a menagerie of unorthodox mechanics (grip, stance, alignment, approach to the shot), ie Barry Pinches.