I did/paid for my test through Ancestry and was able to upload it to MyHeritage for FREE, but you can't do this the other way around. For me they have worked really well, and as well as finding my biological father I have found lot's of other family that I'm now in touch with. As I understand it, they are both accurate (were for me) but MyHeritage test slightly differently to Ancestry so you may get more/less matches on each site.
