In my openion both command do the same thing one shrinkfile will shrink single file while shrinkdatabase will shrink the set of files in the database. Also after executing any shrink command no need to do the full backup but on saffer side you can do it.

Also shrink command won't do any blocking or hold locks(Might be temporarily it can). BUT SHRINK COMMAND IS RESOURCE CONSUMING AND CONSUMES RESOURCES (CPU - MEMORY) OF THE SERVER HENCE ADVISABLE TO EXECUTE ON THE OFF-PICK HOURS.