Seriously though probably the Ebionites or the Marcionites, both throw interesting light on Christianity's first century. The former still followed the Law, championed James and reviled Paul; the latter were Paul stans who went the opposite way and rejected the Old Testament, were the first group to collect the letters of Paul and carried around a Gospel some think was the basis for gLuke.
It seems very unlikely that the Gospel of Marcion was the original version of the Gospel of Luke. This is because there is an overwhelming consensus that Luke-Acts is a joint work, made by the same author, and Marcion did not at any point include Acts. Of course, I’m hardly the first to point that out - Irenaeus best me to it by almost two millennia.
