They are all fine. There are plenty of little girls with those names so none will cause her to standout or be poked fun at. Personally, I prefer Matilda and Bethan as they sound more timeless, classic and grown-up and seem more distinctive than the Ella/Ava/Isla/Eva and Molly/Poppy/Daisy/Milly names in fashion currently. That said, each is a fine name!
If you're looking for other similar names, it's worth checking out the top 100 or so most popular names in the UK because, if you like those 5, you're bang on trend and you'll probably stumble across a lot more that you like. The ONS web site has the data but I quite like this web site's combined spelling list: www.britishbabynames.com/blog/combined-spellings-2011-girls.html
If you're after something a little less mainstream, you might like to consider Polly, Tansy, Carys, Tegan, Elin or Ellen, Catrin, Elodie, Eleanor, Nancy, Willa, Ivy, Zoe, Audrey, Helena, Sally, Naomi, Stella, Arabella, Mirabel, Mabel, Cecily, Hilary, Elizabeth, Elsa, and Estelle.