Most the fighter subclasses are pretty close on the balance factor in actual play. Even the champ is close behind despite the complaing. Im not so sure about the purple dragon though. But I wouldnt worry about which ones better or stronger. Just play the one you like.
It's too bad that maneuvers have been relegated solely to the battlemaster as they provide a useful platform for building subclasses.
The result is subclasses where you end up saying "I'd rather play a battlemaster"
Purple dragon is pretty awful. For a support fighter it offers little in the way of support. Still very playable though, the core fighter is a strong combat class.
I believe the Cavalier is an upgraded version of that - any comments?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.