In the recent versions of MSF for CMMI there's a new work item type: Feature.
Theoretically, a feature contains some requirements as its children and, it defines a portfolio.
While integrating with project server, is it a good practice to use just Feature and Task work item types for sync?
I would start by sating that it is not good practice to sync with Project Server at all. However if you must...
You should not have hierarchical requirement's in TFS. So Feature gives you the ability to break Feature into Requirement into Task. So in that case you should sync all three levels.
If you look at the recently released Safe templates you should see Epic->Feature->Requirement. Accepted convention is that Requirements fit in a single iteration, Features fit in a single release, and Epics are bigger
So you can look at it as a scoping thing. If you are using project server to manage non-engineering work then you want to sync whatever is in scope for your project and sync it below the "Engineering effort" project task. Most orgs sync to the level of Requirement but not Task.