Can you tell me what is the best benzodiazepine?

There is no "best": Benzodiazepines all work on the same receptors, and pretty much do the same thing. Some are short-acting, others intermediate, others long-acting. Some are rapidly absorbed, others slowly. Some hit the brain very fast, others much more slowly. If you want something for temporary anxiety, a rapidly-absorbed short acting drug (like xanax (alprazolam) or ativan) may be best, for gad, Clonazepam or librium.