I Like Pussers. Mount Gay. Bacardi Select Dark. Cruzan Dark... but honestly the smoothest, best/strongest dark rum is Goslings Black Seal. It's a Bermuda Rum. I've been to the facility... just a great company. Sip it over ice... or if you have to mix it, do so with Coke Zero (no seriously) because it's VERY sweet, using coke is too strong, diet coke is OK (or better lime diet coke).
Or you can go traditional, and make a "Dark and Stormy." Using Ginger beer, and Black seal rum.
Black Seal® | Gosling's Rum
If you make a fresh ingredient Pina Colada with goslings it'll look terrible, but taste awesome. Probably the best island drink I had was sitting in Grotto Bay, eating a Mahi Mahi Burger, sipping a Pina made with Goslings (and I am not a big Pina Colada fan, but that was a helluva - yep - breakfast).
PS: Asking a sailor what is the best Rum, is like asking who has the best boat. Oh and that is a clear bottle, the rum is THAT dark.