a simple search should get you plenty of hits, but here is the summary
sharpn rom is relatively decent, but old
cacko rom is a patched up sharp rom...much improved
tkc rom is also a patched up rom, but it hasn't been work since soon after 3.10's release.
OZ has lots of eye candy and lots of features. Though generally thought of as less stable, the 5500 version should reasonably good. Probably good for getting your hands dirty
pdaxrom is generally not for the 320x240 zaurii. I'm not sure if they ported it over.
Each one is loved for different reasons.