Series X. Just about everything but the PS5, really. This is because the PS5 is the only straight TV console on the market. Switch is hybrid, the Series X can easily be treated as the opposite of a dedicated console due to how easy it will be to play its games elsewhere. This may or may not result in big things down the road, but it partially depends on how people warm up more to streaming (honestly, I hope we don't because of game preservation but I have a feeling that it'll happen). Not actually needing a Series X to play the Series X though? That can really be a big deal. Either way, once again the Series X has the better hardware of the two meaning ports and multi-platform titles will tend to be better.
If I'm honest though, if I get one this generation it'll still be a Switch. Next to nothing really interests me about either other console, except the Series X's backwards compatibility (looks like the focus is on the 360 according to some things I've watched, which is very much appreciated considering the RROD).