Canonical releases a new ubuntu every 6 months and time to time it does a LTS (long term support) release which is suppose to be most stable. So far Canonical made 2 LTS releases: Ubuntu 6.06 dapper and 8.04 hardy. Ironically,in my personal experience , they are the worst releases of ubuntu. In detail I am having lots of program crashes in gnome and I am not even telling what happened when I first turned off my computer after upgrading to hardy. In general ubuntu releases have hiccups at very beggining and after 1 week from the release they run quite good. But this didn't happen with hardy. Today, I made a simple google search that verified my thoughts.
I googled ubuntu xxx "worst release" where I put, dapper, edgy, fiesty, gutsy and hardy . I know this isn't a relaible test. But results were almost all telling dapper and hardy worst releases. I saw 1 search result for fiesty.
Dapper actually was the first release that ubuntu maturized. Before dapper ubuntu had 3 releases called: warty , hoary and breezy ( I am not selecting the names!). They were nice but too amateurish (frankly I never used warty but I started with hoary but I guess same applies to warty). Dapper were 2 months late to it's normal schedule. And it was so terrible that canonical released an 18.104.22.168 version. And july 3, 8.04 will give a 22.214.171.124 release. And both of these are LTS and both are terrible.
Earlier I was using Suse 9.3 till it wiped out my disk. When I switch to ubuntu I really like it. They become a major push for innovation in my honest opinion. And I am delighted with its great community. I use Ubuntu since 2005 as my primary desktop machine. I've upgraded my current laptop as 6.10 -> 7.04 -> 7.10 -> 8.04 without formatting almost 1.5 years (which is some achivement compared to windows considering you have to format it every 6 months and pay another licence fee every 3 years for a new version!). However it seems this time I am going to give opensuse 11 (on gnome!!!) another shot.