While I'm not an experienced tripper I'd recommend trying to work through it yourself. Yes it can be very hard an unenjoyable, but if you learn to beat negative thoughts and feelings by the power of your mind alone, bad trips can quickly become a thing of the past as you will forever know how to beat them.
I've personally only had 2 "bad trips", both of which I brought myself out of myself. The first one was on 4-AcO-DMT, the experience wasn't negative or bad as such but I got stuck in a 7-8 hour thought loop that felt like it would never end, it was very scary, eventually I just let myself go with it, and finally broke out of it.. when I did I felt amazing and the last 2 hours of the trip were worth all the fear I endured for those ~7 hours. My first 2C-E trip the other day started out bad, I initially dosed too low and there was an intense dysphoria, I actually felt very depressed, so I just took my mind off it by doing something creative -
http://www.neave.com/imagination/ in particular, along with some cheery music. Soon I was really enjoying the low dose experience, comfortably enough to up my dose and have an amazing unforgettable time
Hope this helps, also, of the two I imagine a fast acting benzo would be best. But in my opinion, a bad trip means there is something the trip is pointing out, something bad about you or your life that you need to change/learn from, even if the entire experience is scary and unenjoyable, learn something from it so that it has been useful to you, and your next experience will almost certainly be very enjoyable.