Vanguard is Briggs. I don't have much experience with the larger Briggs motors, but haven't heard much bad out of them. I have 7 Hondas from 5.5hp - 24hp and all have been good engines. I have owned several Kohlers and they are very good also.
I think it comes down to a matter of perference. I have a Kohler 18HP sitting in the garage I have to rebuild the carb on and get it ready to go in case something does happen to my Vanguard 18HP. The Vanguards are cheaper in price though.
I have a vanguard and a honda I use on the daily. I love the vanguard. Its actually on a hydrotek. The thing has ran like a tank. Hardly any probs out of it. Honda has had a few problems lately.