It depends.
If you don't want to invest huge amounts of time I'd go for Blitz Basic (it's freeware now IIRC so you've got nothing to lose in trying it). You can do some quite complicated things rather easily. It's fun to mess around with, and you can dip in and out whenever you want.
However Blitz Basic won't really satisfy you if you have bigger aspirations, while there have been some applications written using Blitz Basic (BlackIRC springs to mind) you're better off with C. There are other advantages such as being cross-platform.
If you do decide to go with C, I have 2 bits of advice:-
1. It's tough, you won't create anything interesting for ages. Stick with it. You won't get anywhere until you understand the core concepts thoroughly.
2. Don't rely on just one book, none of them cover everything, and there are various ways to skin a cat. The biggest mistake I made when learning C was that I only had one, book which it turned out missed a lot of important stuff. It always helps when you have differing explanations anyway.
