Capture three touches, not one: First (immutable, set at record creation), MQL touch (what converted them), and Latest (most recent before the current stage). First and Latest are two fields; everything in between belongs in campaigns, not in a source field.
Choosing one model forces a false trade-off. First touch tells you what generated awareness, Latest tells you what closed the loop, and the MQL touch tells you what actually qualified them — three different budget decisions. Multi-touch is captured through campaign membership, then rolled up to the deal from the primary contact.
Every claim above comes from work LeanScale published. These are the sources.