I love my Micro Swiss dual gear extruder. I have some homemade filament made from PET bottles that won’t print on a single gear extruder but prints perfectly on the dual gear extruder.

I have a couple S1s that I like. They don’t have a built in fan or hygrometer like the new ones, but they seem to work. You can print mounts for cheap hygrometers if you want (not necessary but interesting to see the humidity change with the dryer running). I usually run the dryer with whichever spool I’m using when printing and it seems to keep the filament in good condition.