Trying to narrow my list of ideas down somewhat by sorting out the similar names!
Out of curiosity, do you prefer [name_f]Lillian[/name_f] or [name_f]Lily[/name_f]?
Thanks 
[name_f]Lillian[/name_f] has a weird association for me personally, but I think it’s a very pretty name. I’d go with [name_f]Lillian[/name_f] and then possibly [name_f]Lily[/name_f] as a nickname?
I’m a [name_f]Lily[/name_f] so I prefer that. I like that it has a more direct nature association and a shorter, simpler spelling.
I prefer [name_f]Lillian[/name_f]. It feels a little fresher and more solid than [name_f]Lily[/name_f], which is rather ubiquitous where I am.
[name_f]Lillian[/name_f] for me. It’s pretty, delicate yet also full of stength
I am always torn when it comes to these two. One day I prefer [name_f]Lillian[/name_f], another I prefer [name_f]Lily[/name_f]. I love just [name_f]Lily[/name_f], but I prefer longer names in general. I really like [name_f]Lillian[/name_f] but I could never commit to it. Until one day I found the french variant [name_f]Liliane[/name_f] instead, which now I have on my long list. I chose because I like it best aesthetically and prefer it over all other [name_f]Lily[/name_f] variants.
Anyway, sorry for not helping! For what it’s worth, between [name_f]Lillian[/name_f] and [name_f]Lily[/name_f] I prefer [name_f]Lily[/name_f] today, but who knows tomorrow. 
I prefer [name_f]Lillian[/name_f], it gives you both options.
Despite being so similar, they feel really different for me. [name_f]Lillian[/name_f] is pretty, old-fashioned, and has a few nickname options. [name_f]Lily[/name_f] is a straightforward flower name. I prefer [name_f]Lily[/name_f], for the nature associations, but if you can’t decide, as others have said, you can do [name_f]Lillian[/name_f] nn [name_f]Lily[/name_f].
Another vote for [name_f]Lillian[/name_f]! It feels fresher than [name_f]Lily[/name_f], and I like that it has many nicknames ([name_f]Lil[/name_f], [name_f]Lily[/name_f], [name_f]Lilia[/name_f], [name_f]Annie[/name_f] etc) whereas [name_f]Lily[/name_f] only has [name_f]Lil[/name_f].
[name_f]Lillian[/name_f], [name_f]Liliana[/name_f], [name_f]Lily[/name_f] all so beautiful you can go with any of them! [name_f]Lillian[/name_f] with [name_f]Lily[/name_f] nick name get my vote
[name_f]Lily[/name_f]. Simple and beautiful.
[name_u]Love[/name_u] [name_f]Lily[/name_f]! I actually find [name_f]Lilian[/name_f] a bit dated/just past its prime and not ready for a comeback, maybe because of the Lilians I know.
I love both. But I do prefer [name_f]Lillian[/name_f] a little more. She feels more classy and feminine.
[name_f]Lillian[/name_f] over [name_f]Lily[/name_f]
Besides being more “complete”, I feel like [name_f]Lily[/name_f] is too simple in sound, while [name_f]Lillian[/name_f] isn’t overly complicated nor simple as [name_f]Lily[/name_f].
You can call [name_f]Lillian[/name_f] [name_f]Lily[/name_f] or or you can call [name_f]Lillian[/name_f] Lill, Lan or [name_f]Lily[/name_f] or just [name_f]Lillian[/name_f] where you can invent nicknames for [name_f]Lily[/name_f], but it’s not the same as having more natural options as nicknames
Oof, tough call.
With [name_f]Lillian[/name_f], the floral association is not nearly as strong, to me. I see [name_f]Lillian[/name_f] as more of a lady-like vintage revival, fitting in alongside [name_u]Evelyn[/name_u] and [name_f]Charlotte[/name_f].
[name_f]Lily[/name_f] definitely pops as a floral name, and seems to fit more with shorter, spunkier classic word names like [name_f]Rose[/name_f], [name_f]Grace[/name_f], and [name_u]Ruby[/name_u].
I don’t really have a strong preference either way, it would just depend on the feel of the name that I was going for.
I’m biased towards [name_f]Lillian[/name_f] because she’s the main character in my novel. However, I think that [name_f]Lillian[/name_f] has more opportunities for names, because she can call herself [name_f]Lily[/name_f], whereas [name_f]Lily[/name_f] can’t call herself [name_f]Lillian[/name_f].
I prefer [name_f]Lillian[/name_f]! It’s elegant, traditional and sweet. I’m crazy about long names and maybe that’s the reason I choose [name_f]Lillian[/name_f] over [name_f]Lily[/name_f].
[name_f]Lillian[/name_f] gets my vote.