Deltarune - "Goats may also get jealous when their owners favor one goat over another."

*You are reminded of this image.

If I had to choose I'd say Ralsei just because you get to know him more. He's a constant companion compared to Asriel who just shows up at the end.

That said, there's no reason to think that Ralsei and Asriel wouldn't act the same in most situations. Just that Asriel would be a bit more experienced given his time with Chara and as Flowey, while the end of Deltarune showed him as more naive.