weld on. bolt on's give you pivot points and will still alow flex.
the only bolt ons I have found that I would have considered are the meier racing ones. they bolt in multiple location so pivoting would be very minimal.
I was still leary about it so I went with MM weld ins. I looked at global west as well. they were tubular. I went with MM because everthing I have got from them was top notch.