the ag1 is based on the a700x while the adg1 is based on the ad700x. the adg1 would be the better choice generally since the open back ad700x has a wider soundstage and is overall slightly better (despite the two having the same drivers... open vs closed is basically the only difference).
check prices for the ad700x + modmic vs the adg1 as well.
the ad-series from audiotechnica have very large soundstages, good positional audio and nice detail. one thing they absolutely do not have is bass extension. many people will claim they are utterly bass-less which is not completely true as they have fairly punchy but not very deep mid-bass but no low level sub bass extension.
the hd518/hd558/h598 series is worth looking at from sennheiser...