I want to get an XT rear and front deraileur. For the rear what is the difference between long and medium cage? And with the front what is the difference between top and bottom pull? What do you guy thinks??

A long cage design allows you to run more than a 34 tooth cog in the rear. Larger gears in the rear = longer cage for the derailler. Medium cage will work for nearly everything out there, plus a medium cage is going to have more clearance. I'd got medium cage personally. I run a long cage on my bike, but I should have gotten a medium cage. The difference between top and bottom pull is just the direction in which the cables on your bike meet the front derailler. If the cables come from the top of the seat tube, then it's a top pull derailler. If the cables are routed under the bottom tube and come up between the stays, then its a bottom pull.

Yes, but with front derailleurs, you also have a top swing and a bottom swing.

Front derailleurs are tricky to order on-line.

L8R