Not really a dark, thats an amber rum and not too great. Albeit Appletons makes one popular reserve aged rum. But not what most people think of as Appletons.
Standard Darks would be Kraken, Old Port, Old Monk, (both east indian rum and widely available here)None are bad choices. By all means though buy the east indian rums on sale instead of the overpriced Kraken.
Steps up would be Baron Samedi, Trader Vics, Myers Plantation, Coruba, Gosling Black seal, Mount Gay, Flor De Cana aged 12 or more (all reasonable choices and better than standard swill.
Better still would be Pyrat, Zacapa, Angostura
Wines and Beyond is a great place and they do some samples if you ask and at different times theres testings for those that really want to try different varieties.
Gosling Black seal is often on sale and probably the best starting point to try a rum with a decent reputation that offers more than a standard rum experience and more complex flavors. Its reasonably priced. Drink that and you know why you never buy stuff like Captain Morgan or Lambs. By all means never buy Malibu, that's what giggling girls or Matthew Tkachuk drink.
For a decent mixer, always on sale, try
Amrut Old Port. A nice dark with complex flavors. Better imo than the better selling Old Monk which is more like black molasses. 25 bucks and you get an attractively unique labeled Black rum that somehow speaks rums days of lore, and that can impress anybody from a novice to somebody that appreciates good rum. Its my darkhorse, pun intended.
Amrut Old Port Deluxe Rum - Review