I solely use the Kensington SlimBlade on my desktop.
It's fantastic especially for general purpose work and browsing, browsing is so much more easier with the SlimBlade, turning the ball to scroll.
The only time I find a mouse more efficient is if doing lots of selecting text and copy/pasting or diagram type apps. I have a backup mouse for when a mouse is more useful but almost never use it.
I was getting minor RSI which is why I originally thought i'd try a trackball. Glad I got one, it's so much more comfortable and wrists / arms now stay relativity still. It's just a shame the form factor isn't that great for carrying about with a laptop.
Another Slimblade user here - it's the best pointing device I've ever used.
The scrolling with the ball itself is a killer feature.
I'm using it for ~2 years now, before I had the expert mouse for about 10 and before some PS2 trackball.
The Slimblade is by far the best - both ergonomically and and mechanically.
(previous trackballs tend to collect a lot of dirt and required frequent cleaning, this one have a hole beneath the ball that prevents accumulation)
I've been using the Slimblade for years. I even contributed a small change to Xorg evdev input driver (the Emulate3Button option) to work around the weird internal numbering of the buttons on the device.
On my couch / entertainment computer I use a Logitech M570, but for work nothing beats the Slimblade.
It's fantastic especially for general purpose work and browsing, browsing is so much more easier with the SlimBlade, turning the ball to scroll.
The only time I find a mouse more efficient is if doing lots of selecting text and copy/pasting or diagram type apps. I have a backup mouse for when a mouse is more useful but almost never use it.
I was getting minor RSI which is why I originally thought i'd try a trackball. Glad I got one, it's so much more comfortable and wrists / arms now stay relativity still. It's just a shame the form factor isn't that great for carrying about with a laptop.