Mac because of the selection. I have always been given great advice by the people working there as well - my impression is that they are makeup artists unlike a lot of other counters where they are 'just' sales people. I could be wrong though
DD1 (20) went to Boots Number 7 for their colour matching and got a lipstick (Brick Red) that looks absolutely amazing on her. I definitely fancy giving their colour-matching service a go now, having seen how perfect it was for dd. Then again, she is 20 and gorgeous, and I am neither of those things.