I disagree with flaw's statement that it doesn't matter which distro you choose.
Yes, it doesn't matter if you only plan on learning. Yes, you can theoretically learn from any distro.
But as any analogy, for a legacy Windows OS, you could choose 95, 95OSR2.x, 98, 98SE, or Me (and maybe some OEM versions in between). In all but a few cases, 98SE seems to be the consensus best choice. Even though in 99% of cases, any of these would be OS-compatible with 3rd party software.
Now all the Win9x OSs are pretty similar. When it comes to Linux distros, the platform is identical (GNU software), but the packaging and administration can be significantly different. You want to choose one of the best tools, not any of the tools available (there are literally tens if not hundreds of official Linux distros).
I think flawedecision really means to say try a few out, and see which you like. That opinion I would agree with.
I personally like SuSE 7.x