I have only used a slimbade for a few minutes but would say it is probably a bit more precise that the old "Expert Mouse".

The slimblade is certainly newer technology (twin laser etc.) but I would probably go for the expert because it is more like what I am used to.

If I was going to do a significant amount of gaming then the slimblade would be my choice, and I would just have to learn how to use it. Not that a trackball would be my first choice HID for gaming anyway.

It's all a personal choice thing, so if you haven't gotten into the habit of using a particular type then I would opt for the latest technology.

Sorry I can't be more positive, but like a lot of things there is no "best" as such, just what is best for the individual concerned.