Four benzos are usually prescribed for the treatment of anxiety: alprazolam (brand name Xanax), clonazepam (brand name Klonopin), diazepam (brand name Valium), and lorazepam (brand name Ativan). The half life of a drug is the time it takes for blood levels of the drug to reach half of what they were initially. Unsurprisingly, half life is closely associated with how long a person feels the effects of a drug. Those drugs with a shorter duration of effects are notoriously more susceptible to abuse. In order of increasing half life: alprazolam (9 hours), lorazepam (15 hours), clonazepam (34 hours), diazepam (60 hours).
Accordingly, I would recommend either clonazepam or diazepam. I would advise that, among other adverse effects, long term use of benzodiazepines leads to irreversible cognitive damage. The best idea is to avoid using benzodiazepines altogether except in situations where anxiety is so severe that it impair your ability to function to a degree that, objectively, taking drugs would directly alleviate impaired functioning.
In other words, let's say one suffers a trauma and can't leave the house because one is so shaken up. Then, administering benzos for a short period would make sense because, although they don't address the underlying causes of anxiety, they MAY provide borrowed time to engage in necessary activities one wouldn't otherwise be able to engage in, while hopefully the person simultaneously improves his/her ability to cope with the trauma through other means (counseling, cognitive behavioral therapy, normal coping and adjustment, etc.).
Benzodiazepines are ineffective, taken for longer than several weeks in a row. Tolerance develops, shortly followed by addiction. To mitigate tolerance and dependence, one should use the minimum, effective dose and taper down or discontinue use intermittently; the best solution is to address the underlying anxiety by whatever normal (non-drug) means available.