Well the main diffrence is one is made by WE and the other is made by TM. Technically I have answered your question.
Now for the non asshole answer.
WE will most likly come all metal.
TM will most likly be plastic, but that is not to say metal versions are not available they just cost more. Upgrades will be numerous for the TM, internals and externals alike.
TM high cappa 4.3 review
http://www.airsoftforum.com/board/in...howtopic=50251
WE high cappa 4.3 review
....nah...Im gona go ahead and let you do some of the work.