Go for the round ones if you like them! I have a beautiful velvet doublet, made as a bespoke jacket for some one else in 1958 that has round buttons. When it came into my care it was the round buttons that caught my eye, they are designed as a targe and are brilliant cut and sparkle against the black velvet. I'd love to locate a couple of dozen of the same to swap the ones on my Sheriffmuir coatee and waistcoat.