Which should I do an embryo transfer on?

So I was thinking I could get that 2 year old stallion I asked a question about and if the vet OKs my mare I could breed her to my friend's horse AND this stallion if I get him. I've given it more thought and was thinking I'd just pay the collection fee to my friend and then just have our trainer help me breed this new stallion to my mare. We'll get some breeding hobbles and twitch her so it will be totally safe. Anywho, I'm wondering who I should do the embryo transfer with. I was thinking I'd ET the embryo with my friend's stallion but I don't know if it would even matter. Or should I just ET them both and keep working with my mare?