There are many things to consider in this. For me, there was no way I would go to a male therapist as men freaked me out to much and I knew I would make little progress in therapy. Fortunately the two female therapists that I have had were both personally acqainted with sexual abuse in their past. They did not specialize in sexual abuse though. However these two ladies have been the best thing for me and have allowed me to heal in ways that I never could have imagined.
To me if you find someone that has dealt with their issues for the most part and is stable enough to model a healthy life, than they are valid to check out. Of course it may be hard to find this out up front.
If they are compassionate and yet professional in their approach, then I would take note of them.
If they are oriented to accomplishing "goals" in healing, they can be very useful. While I didn't know what goals I really had when I first got into therapy, we did come up with some and it was very good after a year or two to actually see how far we had come on those. It kept us focused as well over the entire course of the therapy which helped both myself and the therapist see what was working and what wasn't.
I think it is important for a therapist to not have a one size fits all mentality but to be creative and to think outside of the box. Often I was creative but it just took a slight little push from my therapist for me to grab the answers that were right in front of me. You couldn't have told me that at the time though.
And I think any therapist has to be extremely patient because this is hard work and sometimes others can see where we need to go before we are able to open our eyes long enough to see it.
There are many things but how I have picked good therapists is very simple. I went to visit them (or talked to them on the phone). I let my survivor radar run at max speed and got a sense for what they were. As I talked to them, I tried to match up what they were saying with what I was picking up. If everything matched, than I proceeded. Maybe I was fortunate to find the right therapist at the right time, but the survivor radar is a very good thing (just sometimes it is hard for us to trust).
I have also had times when these same therapists said something or did something that hurt me indirectly. What I have learned is that by confronting them (eventually at least) that I have healed and grown as a result. Often times they did not pick up how it affected me and meant absolutely the opposite of what I recieved. That gave us both a good opportunity to build trust, learn and for me to heal. So not everything about therapy is going to be smooth between you and the therapist (but, but, but, this should be the exception and not the norm).
Go with your gut feeling and continue with your gut feeling. If something isn't right, let them know or look for a different one. Not every therapist is right for every survivor. Each person is different and we connect in different ways.
These are just some thoughts and things that I have used over the year. My former therapist and I stay in touch from time to time which is nice. My current therapist is more new at all of this but she is learning and so am I.