Clonazempam lasts a few more hours that alprazolam and is also less prone to give you any kind of annoying side effects, although the side effects are quite minimal for occasional use, and both (Alprazolam and Clonazepam) are by miles better than diazepam.
I know this from a long experience with anxiety coupled with frequent panic attacks.
But, if you do have a panic attacks, having 2 (or up to 2 more, depending on the circumstance) shots of alcohol is almost a chemical substitute to any of the benzodiazepines (albeit inferior). This is a quick fix, but it can help.
Of course, if you don't want any medication for a panic attack, which is understandable but not necessarily the quickest option for relief there are plenty of good tips here (be warned that this process can be frustrating, but works to an important extent if you train your mind enough):