RFT is more advanced and object recognition is more powerful than ROBOT. In RFT, you have the concept of "Application Map" similar to "Object Repository" in QTP. It is more convenient to use RFT than Robot, especially while working on Web and Java applications.
IBM is also more keen in marketing RFT than Robot, since it has the potential to compete with QTP.
If you get a chance to learn it, dont let it go away.
RFT you should know little about .NET & JAVA, and more over it supports till latest microsoft .NET Frame work, but Robot supports only upto 1.1, am facing an issue with one application where Robot doens't work for Frame work 2.0 so am evaluatiing RFT.