Look for drives that are physically small, spin fast, have fast seek times, have large buffers, and a long warranty. The MTBF stat is useless for comparison purposes. Of course, capacity is the main issue for most people. So I guess the ideal drive is 9 GB, 3 ½" by 0.75" high, spins at 7200 rpm, seeks at 7 ms, has a 2048 KB buffer, and a 5-year warranty.
Drives that spin at 3300 rpm and have 64 KB buffers (like Western Digital drives had for quite some time) have been my "gotta hate" drives for many years. My latest "gotta hate" drive is the Quantum Bigfoot, a step backwards in technology, it spins at 3600 rpm and is 5 ¼" by 1" high. Poor performer. Just remember that hard drives have warranties, your data does not.
Floppy disk
The floppy drive of today is a big joke. When the 1.2 and 1.44 MB drives arrived, the 286 and 386 were power PC's, and a 2 MB system was an overkill. An operating system shipped on two or three floppies, and fifty of these disks could back up that enormous 80 MB hard disk. I haven't used my 1.2 MB drive in a few years. The 1.44 MB disk drive is necessary for booting and file portability.
3 ½" 2.88 MB drives are available (I think IBM is the only one that uses them extensively), but since the floppies are so expensive, they aren't worth the extra cost. I remember seeing a box of 10 ED disks (as they are called) for $40 when they were introduced and just about lost it.
360 KB and 720 KB drives are things of the past, and even I do not remember DOS 1.0 that introduced a single-sided 160 KB drive. Here's some floppy disk humor. Try this command: format b: /s /f:160