As long as its USB 3.0 or eSata , rest don't matter (unless you don't have ether then usb 2.0 can do but its much slower)
You can get 100 replies praising or cursing HDD companies, but since no company want to release failure rates personal experience is pretty much speculation.
at moment 1TB is at bad price range you can buy 2TB drive for same price as 1TB 110$ right now.
Go for 3.5 drive, unless its for laptop and you plan carry it in bag, 2.5 be more convenient size wise.
Go for 5400 or 5900 cooler drives as well
my 2.376 cents