I need to call my reporting engine from sharepoint workflow. What's the best way to do this? It has been suggested that I use a web service, but what other alternatives are there, and how do they compare?
It depends on the interfaces your reporting engine allows, and what you can do through those interfaces. Web services are pretty much the way to go though these days.
Other options would be connecting to the database directly or using come kind of Distributed COM setup; neither of those are a good idea in most cases.