Oda uses both systems though. Color spreads count Luffy, while everything else counts the crew joining order.
Regardless, there's going to be 11 people total on the ship when its all said and done. 10 friends for Luffy. A football team. A family. Etc.
To back that up, look at Chapter titles 68 "the 4th member" (referring to Sanji) and 439 "the 3rd and 7th person" (referring to Usopp and Franky).