It'd have to be T first; the AI would have been trained on Progenitor. In-game, we'd likely see each of these referred to as "strains" of T, despite the possible wildly different effects and outcomes, since naming tended to be generational in the RE series. Or, one is T, one is G, and the others are dead ends; and development continues on those that show promise for B.O.W. or life-enhancement applications.

Technically, the T-series was the only one that was intentionally developed, I believe, and G was a natural evolution of the virus within a specific host.