I've used both daemontools and monit in anger. For a single server that I'm not particularly concerned about, monit has been more than sufficient and convenient. The web interface to see what's going on isn't bad either. On the other hand, it can send me annoying blizzards of emails when things break.

For the next project, I'm going back to daemontools, for a multitude of reasons. Between the /service directory and the svc command, automating stuff is ridiculously easy. I can get the active health check stuff by writing a ten-line script that does a much better check on a server than the generic checks monit provides. I can get emails when bad stuff happens with logcheck.

Daemontools is just so goddamn unixy.