Sub for Gladiator

What would be a good subclass for Gladiator?

Well...define good.
Any class that is compatible will work.
So it just depends on what you want to play. I believe.
Unless there is some type of benefit from subbing certain classes.

I think all u need is + focus + atack speed. So, decide for yourself. :p

The only thing you want to keep in mind is your gear situation. If you want to use all the same gear, BD is the next closest. Then again, after playing a dual using class for so long, why would you want to do another one.

Just pick whatever you want.