There are quite a number of different touring companies which do tours starting and ending in the Hunter Valley. If you have a look at this website:
it gives you a list of those that operate within the Hunter Valley. We're a big fan of wine country limousines and with 6 people it actually works out to be better value than the minibus tours and we get to select the wineries we wish to go to.
As to which one is better it will depend on what type of experience you're looking for. If you're into wine and want to try the out of the way places then a smaller boutique tour would be best, if you're happy to go along in a big group and try mainstream wineries then something like the Cheers Bus would be better.