There is no best -- what works best for you is what works best. You won't react like me, I won't react like you. Imipramine did help with my panic attacks, but Paxil worked much better. On the other hand, imipramine stopped working over time and Paxil kept working better over time, but the side effects also increased over time, whereas once the sedation passed the side effects of imipramine were constant, if very irritating (that dry mouth can be a pain, but not compared with anxiety attacks, I guess). The big difference was, quitting Paxil killed me, and quitting imipramine was easy. But that was me, and again, I'm not you. As for klonopin, I've been on it for years, but I can't it's ever helped much. But again, that's me, you may have a completely different response. In other words, there is no answer to your question but to try something and see if it works. And the only cure isn't found in drugs, though where it is I haven't a clue.