Reddit is a much more mature software, more stable and refined. But it also has u/spez and beside that a generally shitty management.
I think it depends on how fast you find out about its issues.

For me as an older user of reddit, and older overall lol, I’m enjoying it here better. Less bullshit to scroll through and so far people here seem more polite overall. When I first joined reddit I’d have likely joined here too. I had previously joined digg and a few others.

I first joined reddit for immigration and expat help. Even now there doesn’t seem to be much of that on here (though I’ll try to help out by moving my content over).

Reddit is closed while Kbin is part of the larger Fediverse. If you don’t like Reddit you’re stuck, if you don’t like kbin you can move around and access the same content. But yes the Reddit apps are more mature by now, although I’m quite liking it on Lemmy so far.