[vim] How to insert text at beginning of a multi-line selection in vi/Vim

I can recommend the EnhCommentify plugin.

eg. put this to your vimrc:

let maplocalleader=','
vmap <silent> <LocalLeader>c <Plug>VisualTraditional
nmap <silent> <LocalLeader>c <Plug>Traditional
let g:EnhCommentifyBindInInsert = 'No'
let g:EnhCommentifyMultiPartBlocks = 'Yes'
let g:EnhCommentifyPretty = 'Yes'
let g:EnhCommentifyRespectIndent = 'Yes'
let g:EnhCommentifyUseBlockIndent = 'Yes'

you can then comment/uncomment the (selected) lines with ',c'