I have used several Linux distributions over the last 16-17 years. For many years, my primary Linux distribution was SuSE/openSUSE. Since 2007, it has mostly been Ubuntu. Starting with the release 10.10, though, Ubuntu's (in)stability had become increasingly concerning. Release 11.04 only made matters worse. Window borders were erratic in their display, transitions between workspaces was jarring, the feel was sluggish, and an update even rendered the system unable to restart!
Initially, I thought that Ubuntu's Unity was playing tricks. It perhaps interfered with standard GNOME in such ways as to complicate GDM, power management, etc. However, I could not invest the time needed to investigate the problems. Then, I tried Linux Mint 11. It sure did not have Ubuntu's Unity, but had (almost) all the other problems that Ubuntu 11.04 had.
For the first time, I then tried Arch Linux. I was impressed! It is a small, fast, no-nonsense distribution, and has excellent documentation — the best that I have seen for any Linux distribution at all. Added to that, it is a rolling distribution! We, of course, have to allow that it is meant for people who are rather technically advanced. My team thought it was too much of a hassle to even set up a `working' development machine.
Two weeks ago, I tried CentOS 6. My previous trial of CentOS was with version 5.4. Its power management was so terrible that my laptop used to drain out in about 1.5 hours. It used to last over 3 hours otherwise.
This time, though, it is Just Good! I installed the so-called `Minimal Desktop' flavor. In these two weeks of exclusive use, it has demonstrated itself to be very stable, fast and predictable. I am very impressed! All going well, I will be switching my team to CentOS 6, as well, in the coming week or so!