Both are good, but I prefer playing lux ... A lot more range. Also, morgana gets banned frequently... Never seen lux banned.

I think it would definitely depend on the full team composition but I would say that it comes down ultimately to the ultimate abilities for Lux and Morgana.

Lux: Long range nuke.
Morgana: AoE Channeled stun.

Obviously the two are great, but I think that the stun in a team fight would be more beneficial.

I play cass/heim alot. nothing is scarier than a fed lux to me in that situation lol

I main both Morg and Lux... and they both have their good sides as well as their bad sides...

Morg: great for farming after soil hits lvl 3.. shield is OP to stop any CC that can be used to ganks.. however if she gets her shield baited out early it can be zapped down and if that happens she is in trouble... Morg does have huge CD on all her abilities...

Lux: Great poke and zoning an opponent out of lane.. her shield may not be OP like Morgs but it can be used agianst spells like ignite which can save your life of your teemmates.. that in its self is OP.. and IF for whatever reason your opponent stays in lane with 50% or less HP when u hit lvl 6 then its almost a free kill... Lux also has very low CD on most of her abilities.. an ulti that can be off of CD in 26 secs and does 700 minimum is op...

but who is better??? i feel most comfortable playing Morg cause IF i get caught over extending i can sheild and retreat.. her flash ulti combo is nice as well.. but nothing feels better then burstgin someone from full HP to a pile os ashes like Lux can do... jungler sitting in mid bush that doesnt know its warded.. with only half hp thinking they are being sneaky for the gank.. snare.. aoe.. ulti.. dead... "ty for the blue buff"...