It really depends on how much space you need on the hard drive. I picked the 500 GB drive because it gave me the room I needed and at 7200 rpm was fast enough for my needs. I stream movies to my apple.tv and have no problems.
As far as how long any hard drive lasts is a guess. I have a hard drive that was in my old MacBook that is around 6 years old and still running good. I like the idea of the solid state drives but they just aren't big enough for me for the price. I do a lot of LightRoom and Photoshop on my MBP so the room of the main drive is good for my use.