It all depends on what you're looking for - I suffer from panic attacks and Generalized Anxiety Disorder and in the past 4 years have been on the big 4 - Lorazepam, Clonazepam, Diazepam and Alprazolam.
-Alprazolam -Acts quick (w/in 10-20 mins), but doesn't last long (Best for Panic
Attacks in my Opinion)
-Lorazepam - Acts rather quick (w/in 30-45 mins) - lasts long, but need 2X as much as
Alprazolam to do the same job
-Clonazepam - Takes a while to act (up to an hour) - lasts long, same strength as
Alprazolam (Best for Generalized Anxiety)
-Diazepam - Not a personal favorite - takes an hour to take effect, weak (10mg=.5 mg Alprazolam or Clonazepam) - but does last the longest