Some guys will ONLY have M2M sex in a one-on-one situation. Others like 3-ways of various sorts including MFM, MMM, FMF. Then there are those who like groups of 4 or more. Some like being watched while having sex while others hate that idea.
What are your ideas of the optimal situation in having M2M sex? Also, what other situations are you also interested in?
Beyond that, there is no "best way".