Is burning trash better* than a landfill? Honestly asking, I don't know and this is something I'd love to be better educated about. Seems like you'd have lots of toxic fumes from burning, which may make it less of a no-brainer.
A combination of high temperature, gas residence time, and various scrubbing technologies can more or less solve the toxic emissions problem from incinerators. On the other hand, landfills will emit huge amounts of methane for decades, and at this point relatively few landfills are equipped to collect this gas.
From a strictly air quality-focused perspective (my professional area), I would say incinerators are usually better. I would guess that incinerators are also preferable from a soil and water quality perspective, but I can't say for sure.
"Is burning trash better* than a landfill? Honestly asking"
I don't know a lot about this, but I do know that the nordic countries all incinerate their trash, and do so with scrubbers/filters that negate the pollution coming out of the incinerator.
Word on the street is that the nordic countries do everything better than we do and are the bright shining example for all things urban progressivism ... so ... I guess it's the right thing to be doing :)
You can burn it cleanly, at sufficiently high temperatures. In the nordic countries, this heat is then going into city-wide central heating networks, meaning it substitutes natural gas or electricity for domestic heating.
* I don't know how to define "better".