Coffee
Stimulant or depressant?
Coffee to start your day?
Hydrating or dehydrating?
While caffeine is a diuretic, it's a weak diuretic at best, (and then mostly if a non-coffee / energy drink drinker suddenly drinks a few cups), so the net effect is still hydrating both on the short and long term, with only a little variation in exactly how much.
See also Chemistry of common things#Coffee