Wedding transportation for guests - shuttle service or uber/lyft?

While I don't have exp with this, I personally would go the Uber route. Reason being that not everyone will want to leave at the same time so this gives guests the flexibility to leave whenever they want rather than at a set time like with a shuttle.

We used a shuttle. Our ceremony was about 30 minutes away from the hotel we got a block at. We had the shuttle arrive at the hotel for pick-up an hour before we wanted guests to arrive for the ceremony, told guests the shuttle would be there 45 minutes ahead of when we wanted them to arrive for the ceremony, and asked the shuttle to wait an extra 15 minutes for stragglers and leave 30 minutes before we wanted everyone there. That way anyone who was ready to go early could hop on, and we accommodated guests running late as much as we could. If guests missed the 30-minute window to get on the shuttle, there were plenty of Ubers/ Lyfts available.

We have a good ride-share presence in our area, but sometimes the drivers aren't the most safety-conscious or timely, and I'm sure there's a handful of guests who aren't tech-savvy and wouldn't know how to request a ride.

Generally guests are responsible for their own transportation. Covering costs is a new trend. While it is appreciated, it’s not required for the couple to do so if it is out of budget. In our circles, next to no one hires an Uber because they provide their own (or a rented at the airport) vehicle or have a designated driver if they choose to drink. I honestly would not worry about this expense or the logistics.

If the drive is 15 minutes and most guests are staying at a hotel, I'm sure they can call a taxi or carpool. You'll be surprised how many guests meet each other in the hotel lobby or rehearsal dinner/ welcome dinner and offer rides to each other. It's nice of you to provide an option though, but generally guests will plan themselves either hiring a car or renting one at the airport.