We decided to go with Idera's SQL Diagnostic Manager[/url]. It is pretty similar in functionality as Spotlight from Quest[/url]. It didn't require any module or service installed on the DB server, which was a requirement for us when we purchased it. I believe current version of Spotlight does not have anything installed either on the DB server.

Both provide a wealth of information for monitoring and plenty of alerting possibilities.

I guess it comes down to testing them and seeing which one is better for your company's needs....