Team Slayer
4 person team, 3 new accounts (myself, Jamie, some kid), 1 old account (Brian)

With Brian's account as the high (26), matchmaking kept serving us some pretty average players. We rolled for hours. These games weren't even close and we made the exact same team quit 3 times.

When Brian left, we replaced him with Nick's new account (15). Matchmaking then went off of the highest rank (Jamie, 24) and started to serve us freaks.

I'm thinking that the matchmaking really goes of the highest rank available ... then uses their win ratio as a secondary criteria for finding opponents.