Level up the Spear

So I like many of you, I Like to explore and do all the side quest. This is my first time playing the game. I finally went back to do some MAIN story line quest. Turns out I can level up the spear lol. I was level 55 when I first upgraded the spear and immediately upgraded the spear to lvl 5. Oh wow what a difference.

This game is my favorite AC so far, I played the first few. Which AC should I play next

EDIT: Last week the PS store had the Legendary AC pack 80% off. 6 AC games for $40