I suppose there's lots of different types of 'best'
Alliterative/Rhyming (I mean I wouldn't do either of the below but they're pretty memorable and kind of funky):
Kristie, Keltie, Kiki and Keisha
Joshua, Jemima, Josephina and Jenevieve
Chloe and Zoe
Themed (again, I wouldn't but I kind of love it):
Atlanta and Sydney (with cousins Dakota and Savannah)
Out There and 'Cool':
Blue and Summerdaisy
Rowan, Jonquil and Saffron
Cleverly funny:
Anna, Eva, Isla and Oscar (no 5th baby to complete the set)
Just a really lovely set of names:
Hugo, Imogen, Natasha and Madeleine
Fenella, Delphi and Orlando
Jesse, Elliott and Amberley