My friend and I live in an apartment in which internet is provided, unfortunately this is not the best. We have wireless and Ethernet capabilities however the wireless is much slower. When both my friend and I connect to the internet using the wall Ethernet outlet we are unable to play Borderlands 2 with eachother, however if one of us connects to the wireless and the other wired then we are able to play. The downside to this is we get a great deal of lag. This is not a problem in other games for us when we both connect to the wall, any suggestions?
Split-Screen or LAN
EDIT: For split screen have your friend sign on to his account on your PS3 so he can still get trophies and transfer his save data back and forth.