vader might have practiced alot, but not against the kind of opponent he would have been fighting during the days of the jedi. i cant see sidious taking out his saber and sparring with vader. hes a great fighter, no question, he can take out humans no trouble, but up against a sith lord who had beaten mace windu in combat and proven himself second only to yoda i think vader is lacking.
and ben would be good with the force, but the light side lacks the serious offencive edge of the dark side. i still say dooku takes it.