Well, B/X D&D was the first RPG I owned, but classic Traveller was the first RPG I played on a regular basis. So, I could call D&D my first love and Traveller my second. Or I could call Traveller my first love and AD&D my second. Or I could say that my first real “branching out” was Warhammer FRP. (We had a few abortive tries at Star Frontiers, Top Secret, free-form, &c.; but WFRP I think was the first that really “took”.) Although GURPS was probably the first game that really rivaled the dedication I’d had for AD&D.
No, I can never give a simple answer. Why? (^_^)