What each model answers
First-touch credits the channel that started the relationship, so it rewards awareness and demand generation. Last-touch credits the final click, usually branded search or a direct visit, so it rewards demand capture and under-credits everything that came before. Same conversion, opposite conclusions about where to spend.
Which to use, and when
We default to first-touch for judging which channels create pipeline, because in B2B the first meaningful touch is the hardest and most valuable to earn. A CRM like HubSpot records this automatically in its Original Source field, set once when the contact is created. To credit the full journey rather than a single step, we layer multi-touch attribution on top, and reconcile platform numbers back to the CRM's first-touch count as a single source of truth.