Short answer: tempered glass is worth the small extra cost on any tabletop in daily use, since it breaks safely rather than into sharp shards. Thickness depends on the table's size and how it's supported.
Thickness
Smaller tables and protective tops over an existing surface can use thinner glass, while larger, unsupported tabletop spans need thicker glass to avoid flexing or cracking under weight.
Edge type
A polished flat edge is the standard, clean look. Beveled edges add a decorative touch and catch light nicely, at a modest cost increase.
Tempered or not
For any table that sees regular use, tempered glass is worth it — it's far safer if it ever breaks, shattering into small, blunt pieces rather than sharp shards.