I would agree that the key thing is to find someone experienced in working with trauma/ptsd. A therapist without that background/experience/knowledge will be less effective, I think, and may even turn out to set you back further by misunderstanding/mishandling what's going on for you.
And then, yes, I personally think it's vital to find a good fit with the therapist. Because no matter how great their experience/training/knowledge, if you don't feel at all comfortable with them, if you don't like them, if there's something about them that really jars with you....and if it doesn't feel like you can develop more positive rapport with them as you build your relationship together, they're probably not the right person for you to do this work with.
I guess also have a think about what you want/need from the therapist/the therapeutic relationship. For instance, humour is hugely important to me. A therapist without a sense of humour or a relationship where we don't ever laugh together...I'd hate it and it just wouldn't work for me. I also like to know that, if I really want or need to, I can text or email my therapist between sessions. I would be put off someone who said from the start that contact outside sessions (apart from making appointments) was a no go. I know this is common for many therapists, so I'm not making it wrong. It just isn't something I'd like.
So, I'd say that once you've got someone who knows what they're doing trauma-wise, the rest is down to personal preference in terms of finding the right fit - someone who you feel you can keep going back to, to sit and do the difficult work with week after week, who you feel a good connection with (or a connection that's probably as good as it can get at the moment, if trusting/connecting is very difficult for you) and who will help you to do the work in a way that suits you.
Good luck!