Which potion/ether/elixir is the best?

[Garlyle]

The recast time for medicine is the same across all items. (I think)

Nope. Elixirs require significantly longer recast timers.

That said, I believe there is no difference between types of items - so all status heals have the same timer; all HP heals have the same timer; all elixirs have the same timer; etc.