There are quite a number of linux distributions which would be suitable and good with accessibility, trying to say if one is "best" is difficult. Sometimes you should be considering what you want the system to do, eg. is it going to be a general desktop system, is it primarily for multimedia, is it going to be a web server, etc, this may influence your choice more. Due to this you are unlikely to get a good definite answer to such a question. Below I make a few notes on my experiences: (please note all these as far as I know support different keyboard layouts and for braille translation you want to look at liblouis, liblouisxml or may be nfbtrans)
Vinux is a linux distribution specifically built for accessibility. Before people start saying about not liking specifically built things for visually impaired, vinux is based on other distributions (debian in the case of vinux 2.0) and only modifies it to be more accessible by altering some of the defaults. As it is based on debian you should be able to use all the standard debian packages, so you shouldn't be particularly restricted in software available for the distribution.
However if you feel vinux is restricting or you really don't want to use something specifically designed for accessibility then you could just use debian. As vinux is based on debian you should be able to achieve the same results with the accessibility in debian, it may just require some extra initial setting up. The advantage of using plain debian is that you may be able to get a better initial set up for what you want the computer to do (eg. if it should be a desktop system, web server, etc).
I personally use GRML, however it really is for those who like the command line and possibly not the best for people new to linux (it is based on debian unstable and so sometimes you get broken packages, etc). Again GRML is based on debian and so can make use of the debian packages.
A significant part of orca development is done on opensolaris and the accessibility integration seems to be good. However you should note that opensolaris is not linux, its based on the solaris flavour of unix. As solaris is different to linux you will find that certain software available on linux will not work on solaris, this tends to be binary packages such as IBM's viavoice. Also opensolaris supports less hardware than linux, but I think this is gradually getting better. Should these disadvantages not affect you then opensolaris might be a good choice.
Ubuntu gets mentioned quite a bit, personally I wouldn't use ubuntu, but for some it seems to satisfy their needs. Accessibility is included in ubuntu by default, but quite regularly there are questions to this list about accessibility not working in ubuntu. Whether these problems are due to the quality of ubuntu's accessibility or whether its to do with the number of users (which quite a number seem to be new to linux) I will leave to you decide by looking back through the list archives and searching the internet. Ubuntu does try to help new users by making things easy, but by doing this it makes it less flexible and should you want to do something outside the defaults you may find yourself fighting the system (this is one of the reasons I don't use it).
There are plenty of other linux distributions I haven't mentioned, eg. redhat, opensuse and all the other RPM based systems, gentoo, etc but I felt it was only fair for me to comment on systems I have actually tried.
On -10/01/37 20:59, Øyvind Lode wrote: