Lili has a variety of builds, all of which can be situationally good. She can adapt to many situations and this makes her a good pick in most situations.

Lili is both a safe pick, can be useful both as a single and a double support and she can even completely counter mele assassins like Illidan,Kerrigan,Sonya...

The support healer build is the all-round best build. it has good healing, cleanse and shake it off as anti-CC and also shrink ray to help secure kills or as an escape mechanism.
Kung fu Hustle is currently overpowered as it lets you use one heal almose every second but it also speeds up ultimate's cooldown so you can even use Jug of 1000 cups every 40 seconds!

The other 3 builds are purely situational and except anti-nuke I rarely use the other 2.
Anti-nuke sacrifices 2 active items to boost blinding wind. This is useful against auto attack damage dealers and usually a single well placed blinding wind can turn a whole teamfight around. The 2 active items sacrificed are not mandatory for any plays so the price to swap builds is not too bad if there is a target worth blinding.

Secondary support is only good paired with a pure healer that needs some extra supportive skills(morales lacks CC and cleanse, tyrande has limited healing and slows help her aim her stuns, tassadar has no CC or healing, a reghar or uther may decide to play without cleanse)

Serpent healer is a worse version of support healer but it allows Lili to go as a solo laner early game if necessary while still having decent healing and good mana efficency without Mana addict