Typography is hard, if only because it's quite subtle until you really start paying attention to it (in everything). How good or bad a typeface may be is irrelevant beyond a minimum quality, e.g. it's kerned well, it has been pixel hinted. It's simply a question of appropriateness.
The reason Arial is often, arguably inappropriately, slated as a bad font is because it stacks up poorly against other fonts in the situations where it's appropriate. Helvetica is more sterile, balanced, and tasteful — it does most of the things Arial does, but better. The only advantage Arial has over Helvetica is at smaller sizes on the web, where the head of the t, tail of the g, and terminal of a help to make the characters more distinguishable (in theory).
So beyond quality, it's about what's more appropriate. Then of course you've got to set it well, but that's practice.
The reason Arial is often, arguably inappropriately, slated as a bad font is because it stacks up poorly against other fonts in the situations where it's appropriate. Helvetica is more sterile, balanced, and tasteful — it does most of the things Arial does, but better. The only advantage Arial has over Helvetica is at smaller sizes on the web, where the head of the t, tail of the g, and terminal of a help to make the characters more distinguishable (in theory).
So beyond quality, it's about what's more appropriate. Then of course you've got to set it well, but that's practice.