For me I most commonly use 10, 13, 15, 17 and 19 - but 12 and 14 make an appearance fairly often as well. The occasional 6-8mm is used for small things, but at this size I have some 1/4" hex end sockets that fit in a screw driver thingy - you know what I mean!
My views on the Halfords stuff mirrors every one elses - their Pro / Advanced stuff is good
Recently picked up their 12 piece set of ratchet spanners which have come in handy and feel of good quality. A majority of my sockets are Torq because I was poor when I bought them, but since they are mostly 6 sided they have lasted and performed well