20" bars for me. Wide bars are better because you have more control over the scooter, this isn't an opinion it's a fact, when I got wider bars on my bike and Goped I could manual sooo much better. Try to doing push ups with your hands touching eachother then do them with you hands straight down from your shoulders.
The only downside of wide bars are weight and barspins, but neither are really that big of matters. Stan did a bar to bar on this massive gap at SBW with 18's and Jonny beat Jesse Mac at fakie bars with 18's. When I went from 16's to 20's my barspins stayed as bad as before. And as for weight, scooters weigh next to nothing so stop being a baby.