It is better to find an editing service specialised in your research area. Some editors may not understand the paper and may change the meaning of some of your sentences. So it is better to find a professional scientific editor in your area. I know it is an old post so this message is mainly for those who are looking for editing services. Not sure what is your field? If is biology/medical ones maybe you can try Zenith Biomedical Editing.... cheap and good quality. They have free sample editing too...