First and foremost, you are not comparing equal heads. The Rainbird PRS-SAM model has more features than the Hunter PRS30. The Rainbird head has both pressure regulation and a gasket that stops flow when the head drops. Rainbird makes a 1804 w/ PRS only, which is very comparable to the Hunter PRS head. Both heads regulate the pressure at the head, rather than installing pressure control for the whole zone. If cost is a factor, I've found that Rainbird is a bit cheaper than the Hunter heads. I've used both, depending on what the customer originally had in the ground, and have found that both perform very well. If I'm installing new heads, I use the Rainbird 1804's because that is what I like.
The SAM feature is used when you have a down hill run of pipe and want to stop heads from weeping out water when the zone is shut off. The easiest way to tell if you should consider a SAM head is to run the zone, shut it off, and look at the lowest heads in the zone. If they are weeping water and you don't want them to, install SAM heads, otherwise you can stick with either a PRS model or a basic spray.
There are a couple of reasons I will install a PRS head over a regular 4" pop up spray head. The biggest two are if I'm installing MP Rotators or if I have a shortage of water for the system and need to control the flow to an exact number. It appears that you have issues with coverage and the PRS will help that in a round about way. You will supply the heads with only the flow they need to reach the distance the nozzle charts state. Make sure you are reading the correct line and purchase the proper nozzles for the distance you need to cover. When doing that, remember, the minimum distance you want to spray is equal to the distance between the heads.