GTA 6 launches on PS5 and Xbox Series X|S, including PS5 Pro, and nothing has been announced for PC. That makes the console you pick for launch the main decision for a lot of people.
What are you playing on, and what settled it? The console you already own, the price, the friends you play with, the controller, or the storage? If you are still undecided, say what you play most and others can weigh in.
Rockstar says GTA 6 needs up to 212 GB of free space, depending on the device. It has not published frame rates or performance modes, so if you have a source for those, link it.