I'd buy both and live with them for a month then sell second place.
Between the L3000s and HP1000s, I'd pick the L3000s, but I listen primarily to rock, pop, folk, and small group jazz stuff. Two things to know about the L3000s, if you don't already--(1) have the seller check to ensure there is no bass buzz, though, it's usually an easy fix; (2) they come with a large black outer box, a large blue velvet box, a small black cord bag, a large tan headphone pull string bag, and warranty cards about the headphones, leather and possibly something else. And I wouldn't buy a re-cabled pair.
As much as I like the ZD, I think it's better suited to drive high impedance headphones. Whereas with low impedance cans I prefer the BA, HD2, Si2A3(H) and EC2A3--though it's a mute point since both the HP1 or the L3000s are low impedance. Damping on the Grados, or L3000s with EC2A3, or BA is something like a 9 and the ZD is around a 5. The bass punch and control isn't as ideal with the ZD--this only applies to low impedance headphones like the Grados and the ATH.