Almond butter balances the pumpkin flavor well.
If almond butter is not your thing, different nut butters work well, too, and alter the flavor.
Substituting Cashew butter tastes similar to the original recipe, and adds a subtle nutty flavor.
Peanut butter is not so subtle in terms of flavor, and is an excellent substitute if you don’t care for pumpkin—it’s also a nice variation on a traditional PB smoothie. If you want the PB but don’t want to mask the pumpkin flavor, 1/2 Tbsp of PB and 1/2 Tbsp Cashew Butter may work well without changing the texture too much.