According to Geoffrey Arnold:
I currently still use GPC 2.0. What alpha/beta release should I download and compile (what is the MOST stable)?
Usually, the latest release - gpc-980401 in this case - is the most stable even if it is denoted "alpha".
If you are running DOS (DJGPP), gpc-971001 - the latest beta - is probably a better choice for you because we have already detected some bugs in gpc-980401 with the compiler's I/O (the generated programs work).
Peter