I love the nickname
Addie, but I agree with everyone else about
Addison. It's not particularly ugly, I don't think, but there are a million other reasons not to choose it. Besides, if you add up all the different spellings of
Addison up, it's really the most popular name of 2006 by far.
Addison is my favorite spelling though.
Adelaide is probably the best alternative I think, although
Adele is nice and hasn't been suggested.
All of your combos are nice, but my favorite is
Addison Maria.