I levelled both so that I could be suited for any situation. I've mained Warrior since Beta and geared that out with Myth first, but as mentioned, Darklight can be worn by both, so my Paladin was quite a way's behind my Warrior for some time until I got lucky with a few Allagan drops for the left hand side. Once my Warrior had all the Myth Armour/Accessories I needed on it, I filled in the gaps on my Paladin (Coronet, Gloves) and eventually Zenith'd my Curtana and Holy Shield. I'm sitting with both at iLvl 88 now as I'm missing level 90 earrings.

It just gives you more utility for stuff, as PF Groups still won't take a Warrior to MT Garuda XM because of double WW's. I also do Coil Turns 2 and 5 as Paladin, for Spirits Within and Hallowed Ground respectively.