The choice is simple.
Most DVD players and DVD-ROM drives can play DVD-R discs and hardly any DVD players or DVD-ROM drives can play DVD-RAM discs.
If you're only going to play them at home on your DVD recorder then it doesn't matter which format you store your movies on. If you want to be able to play them in other players in your house, or you want to be able to lend them to friends and family or you want to be able to use them in your PC then you should choose DVD-R.
Apart from anything else, DVD-R discs are much cheaper than DVD-RAM discs so why waste the extra money to store your collection on DVD-RAM.
As for the lasting forever thing that's nonsense. DVD won't last forever any more than VHS has done. Sooner or later we'll all end up moving on from DVD to yet another format. After all, now that we can store several albums of music on a little memory chip the size of a postage stamp with no moving parts, how much longer is the CD going to stick around? In 10 years the idea of spinning little discs of silver plastic might well seem as old fashioned as spinning large discs of black vinyl does now.
Murray