I came to Strictly in series 4, so can't comment on anyone before that. However, I'd say Louisa, Emma, And Rachel were better than Lisa (IMO Rachel was the best dancer of series 6 and on technique alone would have won, but I can see how Tom's personality and enthusiasm beat Rachel).
I also think series 5 was a very strong year for the females - aside from the Alesha juggernaut Gaby and Penny were pretty good. And as for Kelly - if she hadn't withdrawn I reckon we'd have seen a Kelly vs Alesha final two, and it would have been too close to call.