I just checked a couple of web sites, and while I think both kittens are beyond cute -- the adult silvers are stunning. So I'd go with the silver.
BUT -- are you sure you can't get two kittens? Cats really need the companionship of another cat. Our local shelters will not adopt out single cats unless you already have a cat at home. If you're cat-less, you take two or none. This is for the cats' own good.
I understand the financial aspect -- I have bassets and they cost $1,000 - $1,200 each, not to mention food, vet bills, crates, toys, bedding, show fees, etc. And we have our two cats, too, who were adopted from a local shelter. Every animal needs another of its own kind at home if there's any way you can work it out. For your future cat's sake, I hope you can bring home a pair of 'book ends'.....