Sometimes I got Morrisons, sometimes it's Tescos. It's more to do with which road I'm driving out of my town on rather than being enticed with loyalty cards. But Morrisons does seem to beat Tescos on a lot of products price wise, though can't speak for Aldi, still in the snob zone
I've got a points card for Tescos, and had the petrol one for Morrisons, but Morrisons have now changed it, you fill out a form and they send you a new form.
2 weeks later I'm still waiting. So this morning I drove off route to specifically go to Tescos to fill up, purely because I've got a reward card and can get a few pence of fuel. So for me reward cards work.