Should I use Pro*C V1 or V2?

Try to make the switch to version 2.0 as soon as possible. Starting with Oracle7 release 7.3, it will be the only version available. The support matrix:

Because Pro*C 2.x behaves differently from Pro*C 1.x, and to ease migration, both versions of Pro*C were shipped with 7.1 and 7.2. I recommend using 2.x or higher for any new development. You can use the PARSE=PARTIAL or PARSE=NONE options to get behavior similar to version 1.x.