[EricH]

Inventor and Solidworks are similar enough that if you know one, you can usually figure out the other. That's how I learned Solidworks: I knew Inventor already (and then I went the other way into the bargain). I'd go with Solidworks if you need complex-ish surfaces (which most FRC teams won't, but other applications, like airplane wings, might); other than that it's a tossup.

Both have tutorials; it's been a while since I used them so I can't really speak to how good they are, but that's definitely a good place to start.