All forms have their pros and cons, although they're pretty similar, it varies due to the weapons you use.
Nevan for example gives you the Air Raid ability along with Vortex, making it a deadly DT form, while Beowulf's power is insane, Rebellion's DT is pretty basic, bland across the board really, once you get better weapons you may end up barely using Rebellion at all.
Oh and, with Rebellion, you can technically fly with it, I can't remember the button combo to do it, but if you jump up in the air and use the right combo, you effectively float for a while.