I reckon you should train melee.
However it really depends on what your target is and what type of account you're planning on developing.
As suggested above, a Range tank is an ideal option and if that's the path you decide to take, then I'd recommend training Defence before Range, however I trained my Range Tank through Soul Wars.
This benefited me in two way; the first being I was able to use a whip and train Defence as normal through each Soul Wars game. The second was that I was able to use the Zeals I earned to level up my Range level.
But if you decide to become a maxed Barrows pure, that's certainly also a viable option.
If that were the case, then I'd suggest training your Attack and Strength/Prayer and then finally train Range.
Anyway, good luck.