For heavy duty use (e.g. car porch, external areas, heavy traffic floors) use homogenous tiles... they are very sturdy and dense compared to ceramics (least durable) or porcelain (more durable than ceramics - it is fired at a higher temperature).

Homogenous tiles are also good because it is 'full bodied' as an earlier poster said.

So many places to get tiles... so far MML, Niro, Guocera = good reviews from friends.