In reply to biggianthead:
As JCurrie says, if heading into the main corrie then the Loch Muick approach is the quickest. However, on a couple of occasions I have approached from the north via gelder shiel bothy, which has a good track for a bike until a km or so passed the bothy. It is a bit longer, but the bike helps, and I think it is a bit nicer than slogging up the landrover track, plus it has nice views into the corrie for a good portion of the way. Probably only worth it if heading to the west buttress side though, and best if the ground is frozen as you cross some peat hags between the end of the track and the corrie.