The two handed weapons are the weapons in the top row of the vanguard class. To get this achievement you will need to get 75 kills with two handed weapons after you have unlocked the second two handed weapon, so that is 100 kills total with two handed weapons for this achievement.
Free-for-All matches can be good for this as a swing from a two handed axe can kill more than one person with a swing, however these weapons are fairly good in all game modes.
Any suggestions for this solution just comment. :D