Yeah I'm enjoying the War Frigate's cannons as well. I'm also maxed in Sailing so don't really need the broadsides.
I personally think there are advantages to all of them...
Sloops - If you want to get somewhere fast. If you want to take out or hunt specific targets (ie. Corvette's, Bulwarks, etc.) it's by far the best ship. Really I'd say for all around leveling it's the better ship.
Galleon - My fav. mainly because of the broadsides. It has the most broadsides of any ship, which means if you know how to use them well you will be a terror at sea. It also holds the most cargo (by a lot!) of any other ship. If I'm in no hurry and want to get some gold this is the ship I'd always take out.
Frigate - This beast can take a hit or 2 with out breaking a sweat. I love using this ship for working on my cannons when I'm alone. This ship holds the most crew, and if you can put together a good crew, you'll destroy ships faster than a ... you get the point
All in all, having all the ships really is the best way to go. You just pick what type of fun you are going to be having that time out and set sail!
