In Ohio, I've been renewing online for a couple years and they've gotten much better (faster). For the past ~2-3 years, I do it online and the new stickers arrive by mail within about a week. I do remember a number of years previously that it took many weeks, to the point that I was concerned it wouldn't arrive on time. I contacted the BMV and they confirmed it was paid for and processed and "in the mail". They offered to email me a letter to keep in the car in case it didn't arrive in time and I happened to get pulled over for something.
As far as the physical BMV locations, they vary from fast and efficient to slow, rude, and hate-their-job employees. Luckily, the one closest to home and work is an excellent location....or was when I last went. I do the mail-order option purely for the convenience.
Ohio has "vending" machines where you can renew your registration. One such machine is in a Meijer's store near me. I have never used it only because of a small extra charge for the convivence of using it. I believe doing it by mail or online also incurs an extra charge? I am retired and just go to the DMV where there is usually no wait and the people are pretty helpful and friendly ( so far anyhow, LOL!)