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.

Too many variables to do a real comparison. Age difference, technology difference, userbase difference, administration difference.

Reddit used to be great, and that’s why a lot of us are here now. It’s not a problem with the technology or userbase (mostly, though past a certain point the popularity can become a detriment). It comes down to the administration, which I think is the only thing Lemmy has got over reddit right now, but it is a major thing.

Reddit, obviously. Way more content and activity. If you’re just finding out about both, you don’t know about the API kerfuffle and the UI isn’t so terrible that someone who’s just getting exposed to it would care because they have no frame of reference. There’s no way the average person would choose Kbin over reddit if they really are just learning about both at the same time.

probably reddit

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.