Shortest acting benzodiazepine is:
Because of its short duration of action, midazolam is the only BZD suitable for sedation of intubated and mechanically ventilated  patients.
Midazolam is a good amnesic with potent and shorter lasting action. It is also better suited for i.v. injection, due to water solubility. This BZD is water soluble, non-irritating to veins, shorter acting (t½ : 2 hours) and 3 times more potent than diazepam. 
STOLE
S - Short acting Benzodiazepines are,
T - Triazolam
T - Temazepam
O - Oxazepam
E - Estazolam
Midazolam
Alprazolam
Lorazepam
Diazepam