When I lock my hubs should both front tires spin when stuck in mud ? Or only some times ?

 

If it's an open front differential, then the tire with less traction is going to spin. The only way both are going to spin is if you add a locker or limited slip to the front diff.

 

Yep..

 

Is it worth putting limited slip or locker in it ?

 

Yes.. either that or a lunchbox locker

 

Depends on what you use it for. If it's a trail rig, definitely. For light offroad and mostly onroad use, you'd probably be fine with open diffs or just a limited slip or locker in the rear.

If money is no object, a selectable locker (air, electric, or cable actuated) in the front would be the best way to go.