I never recommend anyone take the bus in Thailand, have done it too many times myself on various trips.
In this case I would take the train down Hua Hin, and then train back to Bangkok and fly down to Phuket. This assumes of course that PG isn't again flying Hua Hin to Koh Samui, then you could fly Hua Hin/Samui/Phuket.
For train schedules checkout
http://www.railway.co.th/search/mainTableENG.htm