Not sure if this is only happening for me but when I party up with people all over the us match making seems to be alot better. Playing with guys on the other coast and its managable for the most part. When I break off and play solo the lag increases to the point most games you can't play them. Playing solo I am allways matched with south america, play in a party with people from the east coast and west cost and we tend to stay in north american lobbies. I just don't get it. Are you punished for playing solo and treated as lobby filler or what? I allways have best selected but can't seem to find a decent game anymore unless I party up for the most part.
Matchmaking goes off of party leader only, for example if you live on the west coast and join your east coast buddy's party you will be in a east coast lobby. MW3 tried to take the whole party into account when matchmaking but it didn't work very well, i think they went back to party leader only but I'm not sure.