In reply to Roberttaylor:
I own and use the following.
Silent partner- very smooth rope feed, big and heavy, designed for the job, better IMO for mixed free and aid climbing.
Grigri- compact, fairly light weight, rope feed depends on rope size etc but generally very good, works well for aid only, and reasonably well for mixed aid and free.
Clove hitch- very compact, very lightweight, good for aid only, bit of pita for free climbing.
There is another version of the clove hitch set up, where you put several clove hitches on a crab with loops of rope between them, you just drop each hitch off as you ascend, this requires a couple of large crabs and obviously opening the gate of your main belay point, not ideal.
The silent partner rarely gets used as the grigri is my first choice, obviously there are potential issues with it but I've not had a problem with it, and ALWAYS USE A BACK UP KNOT, whichever set up you choose.