Want to play the meta? War.
Want to play for yourself? Whatever you prefer.
Want to play everything? Do it - nothing stopping you levelling both.

I levelled PLD then WAR - was focusing primarily on PLD before SB, then swapped to WAR after experimenting with PLD's new toys. WAR has since become a much more enjoyably smooth experience and has become my tank of choice. Like all games with constant changes, this may once again change in future.

In short, things can change at any time. The more you have levelled, the more you can dive right in. DRK may one day become king - you just never know.