Have been on Tango, Woodys boat and Dive Time all are fantastic with plenty of deck space and decent skippers.
www.tangoofweymouth.co.uk
As for dive sites it all depends on what depth you want. The M2, Sidon and P555 are decent although I'm not one for subs.
Aelion Skye in about 30m
My favourite has to be the Salsette and black hawk stern both with depths down to 50m. Talk to the skippers they will advise you, also have a read of dive dorset theres plenty of info in there
HTH
Andy