I think Lorelai makes the pronunciation clearer, but
Lorelei looks much prettier, more "complete", and mythological-magical. I'm afraid
Lorelei is one of those names that is destined to be misspelled no matter which version you pick anyways!
But, look on the bright side - whichever you choose, you're bound to get both spellings out of it when people try to write it for themselves. So you get it all! :)
I love
Lorelei but it is a hell of a name to find a nice combo for (in my opinion). So I'll just throw some random ideas out there, and maybe you'll be inspired:
Lorelei VeronicaLorelei AmeliaLorelei AdaLorelei EleanorLorelei SophieLorelei JulietLorelei RoseLorelei MelindaLorelei EliseLorelei Elizabeth,
Lorelei ElisabethLorelei StellaLorelei MaeveLorelei Eve