Stamblades have access to all the buffs they need via their class skills or wpn skill lines. The DK skill molten armaments provides increased heavy attack damage but that might be about it. Stamblades have really strong buffs thanks to grim focus and the increased damage after incap.

Thanks. So, besides DK, are there any other buffs that can be given from a sorc, templar, or warden?

Thanks all for the replies. This is by no means a complete list, but these are the ones I found in char planner. Most buffs in this game appear to be self only.

For Wardens, there is Frost Cloak (Physical/Spell Reisist and Minor Protection 8% Dmg reduction) and Enchanted Growth (10% Stam Recovery) from Wardens.

For Sorcs, there is Lightning Splash Conduit for splash AOE damage.

For Templars, there is Spear Shards for Stam and Stam recovery.

Dks have Igneous Weapons as previously noted.

So far, I'm leaning Warden or possibly Sorc (I need to see ahow much conduit works out). I already wanted to level both classes, but I am trying to figure out which will be more effective in the Duo.

Run as a tank or healer (which may influence your choice of class) but get the Undaunted synergies as a priority. You won't be applying those from your end, but they'll be there to be taken. Check out what's in the weapon lines, too. It's not just class that provides buffs/debuffs.

Which reminds me, de-buffing the target improves the allies' damage . You don't always have to add at the giving end.