hey resim i've recently looked into this same thing.
rhino liner is a softer more rubbery liner it is best for trucks that will have a camper or touneau and won't be exposed to the sun
lineX is a very hard bed liner it last a LONG time. it is best for trucks that will have their beds exposed or be carrieng cargo that would rip up the rhino lining
as far as the rust goes most guys will take off any surface rust durning the coating process. the liners themselfs will keep the rust from coming back by blocking all water that can get to it
but lineX and rhino lining will set you back about 1000 dollars depending on what you want done