AFAIK, VSTS has no work item hierarchy still. You can't do parent-child connection between work items. It should be only in VSTS 2010 ;)

- RTC supports heterogeneous environment and multiple development environments

- RTC is easy to setup and administer.
o TFS is a complex beast to setup and administer. Takes about two (2) days to install and configure the entire system.
o Process configuration requires sys admin skills
o Normally, when something goes wrong with installation, you have to clean up the entire system. The problem is Microsoft tries to use too much automatic installation

- Team and access control setup are done in Team Foundation server and Sharepoint server, requires some system admin knowledge

- RTC has multiple editions, floating licensing concept, multiple databases support

- RTC support different collaborative development scenarios (single stream, multiple streams, etc.)

- RTC has fine grain source code change-set management
- RTC provides process assistance and process roles
- Team member and activity awareness in RTC
- WAN performance is better in RTC
- RTC: View multiple pending changes and work with conflicts from one central place
- Quality of VSTS is low, crashes a lot
- Source control system is more primitive than Jazzs
o Only support one change-set at a time
o Source changes are managed at the file-level
- No native use-case modeling support in TFS

RTC support multiple change set and also the ability to suspend and resume any number of change sets. This provides you with a way to isolate your tasks from each other and also to switch from one task to another. For example assume you are in the middle of an enhancement and a high priority requests comes in. You can just suspend your current work ( its take out of your sandbox ) work on the new request and once you have delivered you can bring back all your suspended work by resuming this. There is no limitation on how many change sets you can suspend or resume.

The conflict ( if any ) are also handled and you have an option of resolving any conflict using a rich compare merge editor or let the system do that for you.