Too hard to pick one, it depends on the task. Maybe I'd go with M-x Occur. Other candidates are regex i-search, registers, yasnippet, kill/copy/(insert)string-r

Too hard to pick one, it depends on the task. Maybe I'd go with M-x Occur. Other candidates are regex i-search, registers, yasnippet, kill/copy/(insert)string-rectangle, etc etc. Also, emacsclient.