Now I always think of the Santa Teresa area as being busier than Montezuma. There are the few intersections where it's busy with shops and people and parking and the strip of stores. They've got a few banks and a lot more stores than Montezuma. (The one intersection I'm thinking of might not be technically Santa Teresa). Plus, I think the beaches are busier too.
But other than those few spots most of town is spread out along a long super dusty road. (The dust is why I stay away from Santa Teresa).
I'd suggest Montezuma: you've got waterfalls in a few different directions. You've got Cabo Blanco National Reserve. You've got beach and surfing seems to have become more common north of town up the beach.
Went to Puerto Viejo on my last trip, much busier than Santa Teresa and Montezuma (felt more like party town).