It's a tricky one, both have rubbish commentators. Sean Kelly could not be a more obnoxious, monotoned, unintelligible twunt and Paul Sherwen just repeats the same sentence that Phil Liggett has said a few seconds before. Gary Imlach is probably the best presenter for his humourous throw-away lines, shame he doesn't do the commentating, it'd be interesting and entertaining.
Luckily, the more I watch and get to recognise the riders, the less I need the commentary to tell me who's who and what's happening!