JSB Pellets, Whats the difference between Express/RS

I recently bought a couple tins of JSB Exacts and was looking to buy some more….. Then things got confusing.

I have a tin of Exact Jumbo Express and a tin of the Jumbo Monsters 25.4gr

They have so many variations like a Monster Jumbo RS but only weighs 13.43gr all the names throw me off.

What do you guys find to work best… I am still waiting to buy some Predators, but was going to buy a few different tins, now that I have a SCBA Fill setup so I can go out to the farm and do an extended shooting session