First you definitely want to go bigger in these ballet flats. I wear 37 Blahnik but 38 on French Sole because you want to make the shoes look 'smooth' (i.e. your little toe not poking out).
Quilted vs. Simple
Simple because I want ballet flats to look, well, similar to the ones ballerinas wear and quilt is adding an unnecessary twist to something already perfected.
Cap toe vs. Not
I have a silver one and it's not capped but I had a white one with black cap (I can't find them anymore at their shop, boohoo!). All in all if you have a 'basic' colour like black, I think cap makes it more interesting but if you are already going for interesting colour like silver, metallic green then no cap.
Also if you go for plain, you want the low cut one, it's not so deep as to show toe cleavage but I think it looks nicer especially if you have nice feet!
I like them cos they are cheap and cheerful but actually I'm curious about the name, my ones are French Sole and the sole says it's made in France so if it's London Sole is it made in London, LOL?