I only have pokemon sword not shield. But really there are only a few differences. Like pokemon you can catch (just like all previous games) and now two gym leaders. Really for the most part the gym leaders you don't battle don't get mentioned at all. (So you can't get their league cards.) That's the big difference. Also there is a difference for the expansions too.
So really I wouldn't say one is better than the other. I would say just go with the game that has more of the pokemon you like better. (Mainly legendary though since the others would be easier to trade for.)
Oh also if anyone else has sword/shield and has a beast ball they don't need I'm looking to get one before tomorrow when the gigantamax ever event ends.