grammar - "I wish there were," or "I wish there was," which sounds most natural?

Given the choice of these two, which sound most natural?

I wish there were something I could do for you.
I wish there was something I could do for you.

If both sound equally natural, I'd prefer the first.

Answer

There are two questions that need to be answered here.

First, is there still the slightest chance that there is something I can do for you? For example, I might think that there is probably nothing I can do for you, but I still need to think about it a bit before I can be sure. In that case, I'll say "I wish there was something I could do for you."

Second, how formal is the language you're using? If there is absolutely no chance that I can do anything for you, and I'm speaking formally, then I should say "I wish there were something I could do for you." If there's no chance at all that I can do anything for you, and I'm speaking in a neutral or informal register, then I can use either was or were.