Harddrive Dependablitiy by capacity RPM wich tends to go out quick and doesnt produce as much heat........?

I have been looking at many factors on getting new HD's either 250Gb a couple of them or a 500Gb and spit it into two partions or likewise with a 1Tb HD but some factors that i have been looking at is LIFE early deaths or how quick they go out depending on size or RPM, not only but heating issue also, its either a few small HD's or one big HD split for organized storage. any advice or does it matter? wich will be the smarter way to go, bigger faster to go out or smaller and live longer or Vise Versa