There is only one answer: Moodle. All of the rest cost money and support from a commercial company costs money so they cut corners by responding slowly. With Moodle the forum support is second to none. Most of the problems are solved within the hour (and they tend to be caused by me not reading the help properly). Quite often it is the writer of the module that gives an answer - can you imagine M$ doing that! Think about how quickly Firefox is updated when there is a problem - compare that with Internet Explorer.
Secondly. Our school tried a Blackboard demo system last year. Some staff put a lot of work into it then, when the demo ended, they lost all of their materials. Whatever VLE system is adopted you need control of it.
Thirdly. Moodle may not be the "best" system (although that is open to argument) but it easily can be. The more people using it the better it will become. Moodle 1.6 will be out in beta towards the middle of this month and, from all accounts, it is very impressive.
Lastly, in education we are forever re-inventing the wheel. Even within departments we go our different ways - often creating very similar worksheets. Now is the time to share and the technology helps. As my gesture towards this goal I offer notes on the AQA Advanced Computing (CPT1,2,3,4,5 and 6) together with a KS4 ICT Revision course. All released under the creative commons blurb. Not brilliant but I am sure that someone can improve on it and then offer it back. Contact me through my account details if you are interested or you can pick them up from http://www.e-subjects.co.uk/