Both good rubbers, Vega X feels softer overall to me, easier to spin with but doesn't last as long. G1 is a "better" rubber but is a tad more unforgiving if you can't swing as hard as consistently
Vega X is one of the Vega series I didn't take much to. I had it on for a while, as a replacement for a R53 I tore halfway a tournament; it felt… wrong. Vega Pro is just fine (as is Europe, for those seeking something softer).
G1 is a wonderful rubber, for me. Utterly reliable, and very durable.