If we count only the mainline games (Final Fantasy I-XV and Dragon Quest I-XI), what is the best franchise, and why?

Final Fantasy, by a wide margin. It has my favourite game of all time, as well as four others that sit comfortably in my top 20. I like Dragon Quest too, just not nearly as much. Final Fantasy just has the more engaging stories and characters, not to mention the music, which again is great in Dragon Quest too, but Nobuo Uematsu's work is just unrivaled in my mind.

Final Fantasy.

Fantasia Final. I've always loved the DQ franchise, but FF has had a bigger impact in a more personal way.

I enjoy both series for what they are.

Final Fantasy, for trying new things.

And Dragon Quest, for staying true to its roots.

I have gaming needs for both approaches, and both mostly excel in the way they do it.

Dragon Quest all the way. Dragon Quest Monsters is one of my favorite series ever.

If this is the 90s. Final Fantasy easily. Last 19 years? Dragon Quest. Aside from 12. Final Fantasy has been shit post IX. Dragon Quest on the other hand keeps getting better. I dare say DQXI is the best in the series.

Final Fantasy through X...Once Dragon Quest VIII came out I prefer Dragon Quest games

Before FFX...Final Fantasy by a large margin.

After FFX...Dragon Quest by an even larger margin.

If I had to pick one I'd go with Final Fantasy. The games are simply more ambitious and have done more to push the genre forward. The Dragon Quest games are undoubtedly well-made and have seen some significant quality of life improvements over the years, however the series has mostly rested on its laurels and relies heavily on tradition. I had bought DQ11 for Switch earlier this year and found myself getting bored of it within the first 5 hours. Not a bad game per se, but when you have something like Final Fanrasy 7 Remake that exists it feels a bit trite in comparison. Of course it's different strokes for different folks, as some people enjoy the more simple approach that Dagon Quest offers. Nothing wrong with that.