Myla - pretty and sweet. I like it a lot.
Paloma - not overly keen but it's nice enough
Blair - not keen. Sounds a bit masculine to me, though I know it isn't.
Mya - Like it but prefer the spelling Maia (for no reason!)
Mia - I know it's very popular but I can't separate it from the silly teenage personification of Bulimia so I've never liked it.
Betsy - not keen. Bit granny-ish to me.
Dahlia - Really don't like this. Don't think it has a pleasant sound.
Nico - Isn't this a boys' name? I love it - but for a boy?
Penny - not keen.
Romy - like it but much prefer Romilly
Aria - Love it. My favourite from your list.
Valentina - Not keen. Bit fussy.
Liberty - quite like it. Sophisticated but pretty.
Unique but pretty is always a tricky one to me - if a name is pretty it's unlikely to be unique, I always think!
Although, from your list, the only ones I've actually come across in person are:
Paloma, Mya, Mia, Betsy, Nico and Romy.
How about:
Amberley, Alyona, Averil, Antonella, Calliope, Christabel, Delphi, Della, Danika, Elektra, Evadne, Elisaveta, Effie, Fenella, Fabia, Giselle, Hannelie, Jessamy, Keziah, Kiki, Keltie, Mala, Mika, Melody, Nikita, Nerilly, Nyah, Oriana, Perdita, Persephone, Rosina, Robina, Rowena, Rhiannyd, Samaris, Tansy, Taryn, Tamika, Vashti, Veda, Xenia, Ysanne, Zeryn