Having owned an Ion (from stock to fairly upped) and an Angel 06 speed, my opinion is:
Angel all the way.
Angel:
If you buy a good set of allen keys, easy to maintain
Faster
Better stock feedneck
Easier board to figure out and work with
Incredibly easy bolt access, for that quick bit of lubing the bolt inbetween cases.
Ion:
Metal so weak that doing up a screw to its full tightness will ruin part/parts of the gun.
With above problem, makes in depth maintenance a risky business, especially for a completely new person to maintaining a paintball marker.
Although, whatever people say about the plastic, the body is really just as strong and sturdy as any other gun, its more of a heavy, thick rubber sort of stuff. Not going to fall apart if it hits the floor.