I have local busses in my factories and I put gears on belt if need is non trivial. I.e. about 6-8 assemblers.
Gears are more packed than iron and may save belt lines, but mostly it is personal preference. Either way work equally from practical or technical point of view. I can not estimate UPS effects. Gear belt saves some belts in very large setups but on the other hand needs more inserter and belt operations than direct feed from assembler to assembler. In my games UPS have never been an issue.