In boating, there simply is no "best" - it's all a compromise.
As far as BBQs, we've done it all.
C22 - Hibtachi! Yup! n our Mark I we made the dinette bed extender, so used that piece of plywood to span the cockpit and grilled on the hibatchi. Great steaks in the 80s. With that size boat, we enjoyed what we could and what we could afford. Ours was like a big tool box: with a latching cover. Once closed, the hibatchi would extinguish the charcoal and we ended up using the same briquettes a few times.
C25 - Charcoal Magma. PITA. The round one. Not half as easy as the hibatchi.
Current boat: green bottle propane round Magma party size, works great, came with the boat.
If I was to choose now, I'd get a rectangular rail mounted propane BBQ. Much more intuitive to use - the shape - and the round ones are larger than necessary for the same amount of USABLE grilling surface, easier to use, more like the shape of your home BBQ, right?. We have a CNG stove, so have to use the green cans, not an issue.