I haven't seen a compelling reason to not go with US as a primary program yet. If you're mostly flying on US that's a strong reason to stick with them.

At the same time, it is important to understand what you want to get out of the program to evaluate the choices you have available.

Is your travel mostly domestic or international? Full fare or lowest available? Single carrier or mixed?

What do you want out of your program? Upgrades on paid flights? Local or long-haul rewards? Coach or premium cabin awards? Lounge access?

How do you plan to collect points? Just by flying? CC spend (and how much do you charge monthly/annually)? Other partners?

Answering these questions will certainly help narrow it down.