I have tried using all the usual cheap and not so cheap briquettes (skinflint) with not so good results, on the advice of many members I ordered heat beads, from BBQ World 3x7kg bags £32.37 and they hit the spot in my proQ excel. I am sure that LWP Rest. Lump wood is very good too and I will be giving it a try soon.
It seems to be a rule that for BBQing you need a quality fuel whilst for grilling a less expensive product will do the job.
(Heat beads are also available through Toby)