I looked at Amazon.uk and they have quite the assortment available. I think what I remember from the 70s was Colgin's Liquid Smoke, what I most recently got is Wrights (both which is there on Amazon). My store didn't have Stubbs, but I've actually had Stubbs bbq (hubby and I used to do a lot of eating back in the day) and I probably would have gotten it instead.
I'd say go for Hickory. Small bottle goes a long way and keeps a long time. BTW, the ingredients in Liquid Smoke is -- liquid smoke. Seriously that's what is on the label.
Mesquite for me is more like forest fire than a smoke I like but it was a big craze for awhile. I think it has it's uses but is not my favorite flavor profile.