A JSP is compiled to a servlet the first time it is run. That means that there's no real runtime difference between them.
However, most have a tradition to use servlets for controllers and JSPs for views. Since controllers are just java classes you can get full tool support (code completion etc.) from all IDEs. That gives better quality and faster development times compared to JSPs. Some more advanced IDE's (IntelliJ IDEA springs to mind) have great JSP support, rendering that argument obsolete.
If you're making your own framework or just making it with simple JSPs, then you should feel free to continue to use JSPs. There's no performance difference and if you feel JSPs are easier to write, then by all means continue.
