RDR hands down! the multiplayer is the best i've ever played, seconded only by BC2, the storyline is epic, it is pretty much a gta in the west but even better, much better targeting than gta, good weapons, dead eye, large map, plenty of stuff to do, and challenges! plus multiplayer challenges and maps. also AMAZING graphics
Read Dead Redemption of course, the western-theme gives the free roam world a MUCH larger feel than the city of GTA. I'd list all the things I love about it, but SirNoobalot pretty much covered it so I'm not going to repeat it.
Haven't played RDR yet, but GTA IV certainly is boring once story mode is finished (the story isn't even that good, compared to San Andreas anyway) even on multiplayer it's boring after a short while, Can't compare them though as I've played just one, but from the looks of it I would say RDR is much better, as factor1 said, the western theme makes free roam alot more interesting and feels larger than just a city backdrop.
