Just two formats with similar names that essentially do the same stuff. -R is the official format, from the DVD consortium. +R is another format developed by some other manufacturers that aren't in the consortium. Both do stuff equally well. Technically the -R has some small part of the disc reserved for a checksum type of information, but this doesn't really matter.
The speed ratings are only relevant to your drive's speed: if you have a 16x dvd recorder, then it'll be able to record at that speed only with discs marked 16x. Note though that sometimes other players can only read discs well if written at much slower speeds, e.g., 2x.
Go for whichever format you like, as long as your players can play them. It may be a little experimental to find this.