SLR is a solid time tested block, positive adjustment, no coil type spring to fail, and great customer service.
Superlative is a dual function block. One end of the adjustment is a restrictive type and the other way bleeds off gas to reduce pressure. I found the bleed off inadequate for the gas volume of 308. Do a search here for a thread with more details.
Never used a jp so can't really say, I think it uses a coil spring and ball detent if I remember correctly.