As others have mentioned, you cant really measure reliability, as all drives are not subject to the same environment and conditions by the end user, and there could very very well be some manufacturing defects thrown into the batter of harddrives.
I have been running Hitachi's for years, I have only had one drive go out on me. And that was my fault. I was using my 15K300 outside of its enclosure. I had a fan going to keep it cool. I bumped into the table, and the fan grille shorted out the circuit board
My laptop has one in there, and I have 10,900hours on it without a problem.
I have had troubles with Western Digital in the past, and problems with Seagate in the present.
The only companies which I havent had any problems at all with are Fujitsu and Samsung, but that could be because my sampling of drives from either is small.
The longest drive I have ran is a Fujitsu 15K enterprise drive, which has been going for 9 years strong.
Two summers ago, I unpackaged a brand new 120MB Western Digital Harddrive, which had been sitting new in its box since 1991. It was a big old MFM disc which I was planning to use to get my 1987 Linotype workstation going. I plugged it in, and within seconds, smoke was pouring out of the drive. I contacted Western Digital, and they did not provide me with any help at all. Not even a data sheet, so I could find out the models of the voltage regulators and micro controllers which appeared to be fried. All they said was that it is an old drive, and the chemicals inside the drive must have dissipated from sitting inactive for so long. Well, I tried replacing some parts, and I couldnt get it going. So I brought it to the scrap yard and I got $0.28 for it, out of scrap metal.
Otherwise, I mean the results will be based on personal use.