I personally think that version 1.90 is a good choice for the stability and basic admin,
and 1.92 for the invaluable "Expression Manager" engine.
BTW, old versions are available here
3 key steps reminder:
backup LS files
backup your database ( prefer PhpMyAdmin export )
backup all and more, again and again
A thing you have to know if after upgrade conditions are not working:
In versions 1.90 and up this replaces question.pstpl AND question_start.pstpl. If you are using an old custom template, you need...