Efa for me as it feels the most classic/timeless (I know Eva’s of quite different ages as it’s very international). I live in Wales too in an majority English speaking area - but I’ve met a few local little Efa’s and I don’t think they have any issues where we live (obviously yes, it will need to be explained in most other parts of the world, but then so do many Welsh names/spellings - she’ll get used to saying “Eva with an F/spelt the Welsh way”).
I find Maeve, beautiful though it is, is super trendy now- as is Marnie, and to a slightly lesser extent Ruby (more 2000’s) and Vivienne. I’ve only met ones under 25 (or quite elderly) which makes me think those names might date. Miriam is more timeless and fine, it’s just not my personal taste.
Have you considered Eve? Mix of Maeve and Efa but has never got quite as popular as those two- feels pretty timeless and doesn’t have any spelling or pronunciation issues. I like its elegant simplicity.