1) The most stable is likely from the stable branch, but that one is stone old and misses in the meantime a lot of features.
I would recommend the svn-1586 version. Around since a couple of months and seems to run rock stable. Also my experience.
2) When it comes to unslung then indeed 6.8 would be the one to take. Theres no point to use an older one or to use a snapshot that you would have to compile on your own.
The alternative if one wants a more recent installation with more options, which would need a lot more time to set up however, is installing debian 4.0r2 (soon).