Which Lilith should i aim for next?

i already have the gunner one (super nerfed) and the blue one that i havent invested in.
i recently attained a beelzebub so red could be horrifically strong but the immunity removal of the green and purple one seems promising in the current beneficial effect spam meta especilly the green one's perfect corruption

any thoughts?

Depend on the rest of yoru team - all of the Liliths have a place. I have noticed a few top players even using the Assassin one which until recently did not feature much at all. I have them all and still use Gunner in PVP even though she was berfed as she works in my attack team as she can give immunity to team at start if you use Life tally (for example). Depending on defence team I use Sent, Mag, Gun and Assassin - just depends but at the moment Guner and Sent are nearly always used.

I would go with Sentinel since you have Gunner and Magus. The Beezel/Warrior Lillith combo looks great and works great when it works but Immunity is king right now and Primordial builds often have Perfect Immunity so you won't land as many chain stuns as you would like. Sentinel Lillith has a great passive that works well in the current meta and can also lock up those pesky Destiny talismans with Perfect Corruption.