Those are my top three gaming series. This is tough
I started with Mario as Super Mario World was the first game I remember playing. The Mario series will always be the O.G for me. I enjoy pretty much everything about it (2D, 3D, paper mario, etc). It excellent mobile & console games with it.
With Pokemon, I played/own more Pokemon Games than both Mario/GTA. It's been 15+ years and I'm still playing it at some quantity. It's my favorite mobile series.
GTA however is my favorite console series, as Open World is my favorite genre, with 3D platformers right behind it. It packs the most powerful 1-2-3 punch (Gta III, Vice City, San Andreas) with IV & V being grand themselves, and has always been the standard for other open world/exploration games since then. The atmosphere, the freedom, the characters, the radio, just all magnificent.
At the end of the day however it's Mario (as a whole) > GTA > Pokemon.