your bound to get tons of bias in this thread..especially on the escapist, most people here are diehard fallout fans and think halo is mostly a piece of shit..
so on topic anyways, id say if your getting both eventually, which is what im assuming, go with reach first, as fallout new vegas is bound to be glitchy and whatnot at first, and they will patch that all up and have some decent dlc to download by the time ou can buy that im sure, while halo reach is that multiplayer and honestly i think its important to be in games like those from the start so you dont start behind and end up being the "noob" who can't keep up with the cheese strategies and whatnot.
but hey your choice, oranges and apples man if your getting both