Depends on what you prefer. If you're just looking at specs, I think the Series X has slightly better specs, but it's not really going to affect your gameplay much at all. And some cross-platform games actually run better on the PS5 at the moment (possibly because developers didn't get Series X dev kits until much later than PS5 dev kits, or possibly because of PS5's solid state drive technology, who knows?).
Do you want a system that has games on it that no other platform does? Then the PS5.
Do you want a system that allows you to play loads of previous-gen games (from original Xbox, Xbox 360, and Xbox One)? Then either the Series S or X.
Do you already have a PC that you game on and you don't plan on moving between the PC and a console to play the same games? Then get the PS5.
Do you want to be able to play all Microsoft Studios games Day-1, along with 100's of other games for a very affordable subscription price? Then get either the Series S or X?
And finally, which I think is the most important question when it comes to choosing a console these days, do you have friends that you would like to play with online? Which system do they have? Go with that one.