Like both names but we are also over-run with Milly/Amelia/Mia/Emilia's. Had one swimming class where it was Milly, Billy, Tilly, Amelia (normally called Milly) and us... it was just a bit... silly. On that basis I prefer Abigail.
Abigail Abigail Abigail! (Might be my name! ) Amelia and Emily were at numbers four and five respectively last year, add to that the Emilias (at 85) and Amelies (58) and it's very popular, if that bothers you. Abigail was at 47, Abbie at 98, so still quite popular. I like Abi for the nickname, with that spelling. Why add letters that aren't in the full version?
As a personal opinion I think they're okay but nothing particularly special. Emilia/Amelia/Amelie's are ten a penny round this way as are Millie/Milly/Mia's, so for that reason alone I wouldn't use it. Abigail is nicer but a bit dated for me.