As far as I know Slackware can be appropriate while this linux distro doesn't bring any modifications to the standard linux kernel.
So you can download original kernel source (from ftp://kernel.org/ or some mirror) add your module, compile it, and nothing will be broken (perhaps )
I'd say gentoo's the most appropriate. It's easy to get all the debugging tools you want, and it manages to be flexible without carrying 9 metric tons of baggage with it; that is to say, you can do things like installing your own kernel without driving the installer absolutely bananas.
I must warn that gentoo is too difficult for intermediate users
Arguable. The instructions are verbose and clear. Also, it will teach you more about linux than any other distro, and if you're not an advanced user, you certainly will be by the time you learn enough to write device drivers!