I think Earthbound is better because the story is better and the gameplay too, I know it's older than Undertale but it's better than Undertale.
I've haven't played Earthbound in some time, years, in fact, but I really like the story curve the game takes, and it's a timeless classic, so I'm with Earthbound all the way.
Even though i've played neither of the games you mentioned, I am going to have to say Both games are good. Both have really deep and moving stories, Lovable characters, great gameplay and are huge staples in the RPG genre. But im just going to say for the record, im going to go with Earthbound here. Mostly because Its a bit more graphically advanced than undertale.
Personally, I prefer Undertale. They're both relatively popular, so I've seen and heard some stuff about Mother/Earthbound, though I've never played it.
I would have to vote Undertale, as some of my friends play it therefore I would obviously know more about it. Undertale for me I guess.
I like both, they both have their good and bad. I'm well aware I RP as an Undertale character, but I still like the Mother series and Undertale equally.
I really want to play Mother, since it looks amazing.... hmm, I wonder which one I like? ««««««««~~~~~~~ Hmmmm..... tough.
Earthbound and Mother 3 is the best franchise of them all. I played the original of them on ROMS and they have a better and longer game plot than Undertale but I also pay respect to Undertale as well for the hard work and cool details and such. Wanna check out the website me and Toby Fox go onto? This is the website and this is Toby Fox's Profile
Undertale is great and all, but here I gotta stick with my roots and say Earthbound, mainly just because of Mother 3. As feels inducing as Undertale is, Mother 3 will always be 5000x more. Even though Undertale is definitely more genre savvy and more stylish, Mother 3 is always Mother 3 and that is all it needs for a nostalgiafag like me.