What anti-anxiety medications have least side effects?
It would be on a person by person basis.
You have pretty much three types of medications that primarily used to treat Anxiety disorders. Those being, Antidepressants (SSRI's/SNRI's/NDRI's/TCA's) Benzodiazepines and Beta-Blockers.
Depending on what kind of anxiety disorder was being treated. (Agoraphobia/GAD/OCD/Panic Disorder/Social Anxiety/etc.)
In most cases Antidepressants would be generally classified as the one with the least side-effects, as with both Beta-Blockers and Benzodiazepines, a few of there most common side-effects are Drowsiness/Dizziness/Blurred Vision.
Knocking it down to just one medication as the "Safest" would have to include what specific type of Anxiety disorder the patient was diagnosed with, and their past history/family history.
Antidepressants (Most commonly used are SSRI's and SNRI's)
Examples of these would be as followed.
SNRI's (Usually these would be the first line of treatment in say Generalized Anxiety Disorder (GAD)
Yet there are also a sleuth of TCA's/NDRI's that can also be used.
Then even further down, these are usually for in cases to help with Panic attacks which would be Benzodiazepines and Beta-Blockers
Benzodiazepines (Note; These are just the most common ones, and not all of them)
Beta-Blockers (Note; Just the most common ones)