Given that Boots typically charge at least 20% more for the stuff they sell than rival stores do, I can't see how using a Boots Advantage card makes any sense at all.
I've got a Tesco Clubcard but I don't go out of my way to use it. (I only rarely shop at Tesco, although I occasionally use one of their filling stations).
I've got a Morrison's More card too, which I use fairly often but, again, I don't go out of my way to use it.
I'm fed up with being asked if I've got a Nectar card in Sainsbury's. I haven't and I don't need any more plastic cluttering up my wallet. (To get to my nearest Sainsbury's I have to drive past Asda, Aldi, Morrison's and Tesco, so I don't get there very often anyway).
I've also got a Co-op Dividend card, which I use whenever I go into the store just down the road from me. However I never seem to build up much 'divi' and I often forget to use the dividend vouchers before they expire anyway.
The best value reward card in my pocket is the Waterstone's one. You get one (virtual) stamp for every full tenner spent, with 10 stamps getting you a tenner off your next purchase.