The right one is the better one of these two, the left one although larger has a dark centre zone, the dark stripes going out on each side is going to look really dead probably. Is the one on the right eye clean? Does it have crushed ice or something weird going on in the pic, see the crystal like parts in it or is it reflecting off something?
The one on the right if I had only these 2 to choose from. The left one has huge black areas which are unattractive (non sparkly). I would want a good closeup on the right to make sure the center isn't dead (looks very see-through instead of seeing the facets).
Mmm, I agree with Arkieb that something weird is going on with the stone on the right as well. Have you seen both stones in person? Like Arkieb, I can see crushed ice in the stone on the right...