Blitz Basic would be the logical choice as it is still available on the PC, AFAIK.
I have both and still plan to learn both of them before moving on to StormC++ and REBOL, then maybe JAVA and other C++ compilers on Linux & MacOS. I bought a programming book for my Son titled "Programming Games for Teens" and was surprised to find out that it was based on, and had a CD inside with Blitz Basic for the PC on it.
Edit: AMOS and AMOS Pro are available for free for a download. If it were not already past midnight and I didn't have this migraine headache, I would post a link of where you can find it. There is still a small group that is running a website for AMOS and a few members of Amiga.org belong to that group.
