So far, my favorite is the lightspeed zulu 2's(sits around your ears, not on them like the a20's or x's) so better for longer use IMO, or qc-15 with Ufly mic. The a20's are good, but being able to use the qc's on their own is great for hotels, commuting, etc. Plus they are less than half the weight of the a20's or lightspeeds.
Iv also used clarity alofts. While super light (3oz total i think), they sit weird on my ears and rub real bad. Also makes ur sunglasses sit funny since they are ontop of that stiff wire that goes ear to ear around your head. Also mic boom is super loose and never stays put. Takes getting used to the extra ear pressure from the foam inserts. They only way for those to work well in terms of noise surpression is to have tight(ish) fitting ear buds.

So my list
1 qc-15 with ufly (cheapest too btw. Headset+mic)
2 lightspeed
3 clarityalofts
4 bose a20/x.