Depends on their build. If it's the usual one shot Large Club DWGR, then it's best to use something like Pursuers to keep them off you and put them on defence, while you can try to hit them with you melee weapon as they exit their rolls. These guys will want to roll bs you most of the time, so use it against them. Bait them to do a roll bs and bs them as they exit their roll behind you, before they have a chance to turn around.
If it's a caster build with DWGR, then spears are the best way to go. Their range won't let them cast and unless you have Mid Roll, or worse, you'll be able to catch up to them, so they can't get out of your spear's range.
If it's the more common DWGR Dex builds with katana and such, then it's best to use a straight sword, like Broadsword, Claymore, or curwed swords to stagger them and perhaps even do some nice combo damage. Just be careful with anything slow, like Claymore to not get roll backstabbed. This can be applied to the rare no Poise DWGR guys. straight and curwed swords destroy these builds.
At least that's what works for me. ^^