I went out via Chicago, and back via LA (aerlingus). I can't imagine there is a quicker way than the shorthop from LV to LA, and then the over-night Aer Lingus to dublin. Sure, theres cheaper, but not quicker. And you wake up in Dublin, not the UK, (with another 2-3 hours of early-morning UK airports before you reach dublin)
Get the AerLingus LA flight for sure.
p.s. LV airport has to be experienced to be believed. From someone who travels a lot, I can tell you this is a whole new world of queuing! When they ask you turn up 3 hours before your flight, even for a 30min hop to LA, I'd take their advice