If you have all three, you should really take the time to judge yourself. But if that's just flat out not possible, well I'll describe all three:
Abyss AB-1266 - The fastest and punchiest of the bunch. Slight V-shaped sound signature, mids are somewhat recessed and unimpressive, treble sounds rather unnatural - some exaggeration in the upper frequencies. Best sound stage and imaging of the bunch. While it has a lot of bass, sub-bass is disappointing as it rolls off earlier than such an expensive planar should.
Audeze LCD-4 - The most laid back, intimate sounding headphone of the bunch (intimate as in the sound presentation is closer). Perfectly flat bass and mid range response. Probably the best bass extension of any headphone (maybe tied with a few others), bass is monstrous but never in front of the mids. Mids are full and lush, treble is quite awful though. It has two treble issues: elevated upper treble response that causes some sibilance (at 'T-' like sounds) and exaggerated cymbals and similar negative effects, but PEQ fixes this easily. The bigger problem is lower treble recession (some will call this upper mid recession but it's the same issue) that causes a very odd, distracting, and incredibly fake sounding veil around vocals, pianos, and some other sounds. It makes it sound as if those sounds are incomplete, travel nowhere and are sucked into some black hole.
Focal Utopia - The most neutral and natural sounding headphone of the bunch. I listened to this one the least of all of these. It has the typical dynamic headphone mid-bass hump and sub-bass rolloff, so disappointing bass as usual for this tech. It has some of the best treble of any non-electrostatic headphone though, I heard no issues with it in my brief auditions of this headphone and it makes it sound more transparent and detailed than most non-electrostatic offerings. The Utopia sounds kind of like a poor man's Stax SR-009... except it actually costs more LOL. Sound stage and imaging are nothing spectacular, bass is one note compared to the previous headphones and high end Stax systems, but I don't think it has any major issues beyond price and perhaps weight.
I hope this helps you choose. I can't point out which one to keep... in all honesty I'd sell them all and get a nice Stax SR-007 or SR-009 or SR-009S system (used SR-009 if need be), since to my ears any of these Stax headphones with a proper amp makes all of those (and any other non-electrostat) sound relatively fake and low quality in comparison, like comparing the Sennheiser HD 800 S to the HD 558.
