Nickel plating is used for a very very durable finish on the keys of clarinets. It won't tarnish easily, or at all if you wipe down the keys regularly, and it is very bright and contrasting with the wood of the instrument.
Silver plating, in my opinion, is softer to the touch and "warmer" in appearance. It does tarnish easily as it oxidizes and turns black. Unfortunately, it is not as durable as nickel and within a few years may wear away in places. Supposedly, silver adds a minute amount of weight to the instrument and thereby darkens the tone, and it is also more expensive than nickel.
I personally prefer nickel simply because it is more economical, and it also more durable. Basically, the choice between nickel and silver is a trade-off between looks, durability, and a slight difference in tone.
Good Luck! Go to the Woodwind and Brasswind to find R13s for about half the normal purchase price.
my personal preference is silver, because it feels nicer (i think). they seem to warm up a little, maybe? some of my keys are tarnished, but it gives it character since the instrument is older than i am, it doesn't bother me.
I like the "white" look of silver and the way it feels on my fingers. It just comes down to what you prefer. Resale value on a sliver-plated horn is probably higher. Buffet use a pretty thick silver plate, and I've seen some old, well-used horns with no complete wear-through.
My first clarinet was renickeled just before I got it. After five years the nickle began to came of. When I played for two hours my whole fingertips where black.
Now I have a clarinet with silver keys. The clarinet is 30 years old (never had new silver on the keys) and indeed the silver has come of on some keys. But I can play easily for four hours and then my fingertips are only a bit greyish.
I can't imagine a music store in my country that would sell even an E11 with nickel keys.
I might sound a bit rude, but just know that I've tried both nickel and silver. It doesn't change anything about the tone and I feel absolutely no difference in the touch, but I do know that my nickel keys where far less durable then the silver ones.
Well, my plastic clarinet is nickel-plated and my wooden clarinet is silver-plated. I feel silver-plated keys win hands down. I just really like the way they feel. Something about nickel just makes it seem cheaper. As a result, I guess that's why silver-plated clarinets are more expensive. If I was going to get anything, I would aim for the best qualities that give the best results.
searching...
since the instrument is older than i am, it doesn't bother me. 
