Differences and when to use which one.
A good comparison document.
Another option is to wait for the High Availability release in Orion, coming soon! If you want to get a heads up, take a look at the Server & Application Monitor BETA forums here on THWACK, or better yet sign up to test the latest SAM BETA and have a go yourself
Whilst it won't give you full DR resilience, as the name suggests, when released it will give you great High Availability protection. Couple this with VM replication to your DR site, along with database mirroring/replication to the same, and you have great protection, without doubling your monitoring costs (with active<>active) or relying on old code (FOE).
