Which gives knowleadge??

It depends on whether an employer has the opportunity for other technologies.

Also note that the skills that are most desired are often reserved for people that have been with the company for a while. So you might not be able to get experience with something that is the most lucrative (has the most opportunity) unless you stay with an employer for a while.

So there are no easy answers. It might be more beneficial to work for an employer with many employees and abundant diversity or a small company in which they need someone that does a variety of things.