I'm a weirdo who keeps both a mouse and a trackball at my desk, but I've pretty well settled on my choices for the two of them. Here they are:
Razer Basilisk V3 Pro: Has virtually every feature under the sun, packed into a very G502/MX Master-like body. Butter smooth on wireless and the sensor tracks on my glass desk. The battery life is only okay, but I just dock it whenever I'm not using it (which is most of the time nowadays). Smart Reel is undoubtedly a gimmick, but it's neat. My main complaints is that it's not made out of PBT - which is insane to me given how expensive this mouse is, and that Synapse 4 is a total resource hog for no good reason. Otherwise, it's about as good of a combination work and gaming mouse that you can get in my book.
Microsoft Trackball Explorer: I bought this and a few other trackballs just to satisfy my curiosity - and I haven't been able to stop using it. It's quite comfortable and the sensor still feels plenty fast for my 3440 x 1440 display. The 46mm ball is just the right size for me and the chrome steel bearings have relatively little stiction. I also like the red glow ring surrounding the ball which really drives home that early-2000s optical mice aesthetic. Software is lightweight, and there's plenty of buttons to map out. This thing has almost completely replaced the Basilisk at my desk for virtually everything except for FPS games. Kind of a bummer there isn't really a perfect replacement for it though.
Honorable mentions:
- Razer Mamba 2015: IMO, still just as good as any of Razer's current premium mouse offerings, minus nearly as heinous of a software experience. I kinda regret selling mine...
- Microsoft Arc Touch Bluetooth Mouse: I freakin' loved this thing for travel. Folds almost completely flat and it feels more natural to use than it looks. The haptic scroll "wheel" actually feels pretty convincing. Also regret selling...
- Logitech Trackman Marble FX: Out of all the trackballs I've owned, this has the best shape, hands down. Unfortunately, time has caught up to it and trying to work with that sensor is just pure pain. One of these days I'd like to try and fix it.
- Logitech Cordless Optical Trackman: Same situation as above - really great shape (but not as good as the FX), old and slow sensor, all made even worse by 27 MHz RF wireless and a 50 Hz polling rate. This thing deserves to be so much better.