I for one will for the most part refuse to play with vanguards. While they can be a force, and I have seen them kick ass quite effectively, there's about a 75% chance that they will be mindblowingly awful, especially humans. Asari I will usually let stay unless they try to play with level 8's on silver, simply because their charge/close range abilities aren't that great, so they have a far less chance of being stupid; similar for drell.
Kroguards...honestly they are so overpowered they should never die on silver, yet they frequently do. I'm hoping time will settle down all the overeager vanguards, as it has for the most part concerning Krogan Soldiers with melee.
I personally just don't like the vanguard playstyle; relying entirely on your ability to kill everything at close range in the area before they have a chance to kill you doesn't appeal to me, I can't bring myself to like Batarians either. Now Geth Infiltrator + HM + cloak + Geth PS... that is a real close range class, people. Quick, efficient, high DPS, and able to easily escape if things get too hot = perfect solo class.