I definitely prefer the
Savannah spelling. People might believe it to be trendy, but only because it's "in" at the moment. It does have a lot of history as a name, so although popular now, it is by no means a modern name, which helps. It may be popular, but I don't consider it trendy, if that makes sense.
I have always liked the name
Savannah. However, I have to say that recently I have started to have a more stripper-ish connotation with it. That said, I still like it but may think twice about using it as a FN.
As for
Lillian and
Brook - I
LOVE Lillian and
Brooke. But
Brooke with an E, for sure.