I found a few writing services and started reading reviews, going through the process I found a lot of positive and a lot of negative ones so I am a bit confused. How do I choose a writing service I won't regret using?

Well, trying out one is the only way to make sure. I myself stick to assignmentgeek now, those guys never disappointed me and I'd say that it would be a good idea for you to try out this one at first, I am pretty sure that you will like it. If you won't, go on testing different services until you find the one you are satisfied with.