Where are you staying? I might be able to point out a decent nightcap spot.
If there's 3 of you going you might as well get a taxi - it'll be about £20 - £22 inc tip (unless you're a bunch of miserable fuckers) to most of the city centre (inc. the airport toll).
The 500 bus is a good option too - about 3 quid each, I think. Maybe less. Stops in Liverpool One. Takes about 35 mins to the taxi's 20.
The 82A bus will go to/from the airport as well but it stops at every single stop and goes through Speke, Garston and Wavertree before going to Liverpool One bus station.
Outside the arrivals door buses to the right. Taxis to the left. A guy working for the airport will point you to the next available taxi.
flying into manchester. no direct flights to liverpool from where i am so it’ll be bus/train from there.
staying at some hostel that’s 5 mins walk from lime street train station so i imagine its fairly central.