Transport from Split to Dubrovnik

Buses are heavily used in the Balkans because the rail network is sparse. Any other option will be much more expensive, I'm afraid. I've used the buses extensively in that area and was always very comfortable.

I can't address your car-rental question.

I took the bus and it was a great experience, complete with beautiful scenery. Inexpensive, modern, comfortable, air-conditioned option. Nothing at all to be wary of.

Here's one private service option (I just found it by a simple google search). I'm sure there are others you can find on the internet.
https://www.viator.com/tours/Split/Private-Transfer-Split-to-Dubrovnik/d4185-5562SPUDBV

EDIT: That price appears to be a teaser rate, and it doesn't take just 2 hours to get from Split to Dubrovnik, more like 4-4.5 or so with a quick stop. Personally, I would take the bus.

Don't get too happy about the very low price shown on that initial screen. I was suspicious and tried a random date in mid-September. A cost of over 350 euros popped up. I don't know whether that would cover one person or an entire party that would fit in the vehicle, but it's exorbitant for only one or two people.

I too would encourage not overlooking the bus. Cheap, efficient, comfortable, better than many trains I have taken. For private transport, certainly there are options, but the cost, to me would be a major issue unless I planned some sights along the way...adding even more $$$.

I get motion sickness easily and one time we took bus in Spain and the winding road made me very ill. So we're trying to see if there're other options available. I suppose taking Dramamine may be another choice.

Are the seats on the bus first come first serve or can the seats be reserved? I think sitting in the front may help reduce the effect.

I know Viator is typically more expensive than private drivers. Rick's book lists a few drivers for transport from Dubrovnik to Mostar so I was wondering if anyone has experience of private driver from Split to Dubrovnik. Getting a rental car would probably be cheaper even with the one-way drop off charge.

European bus tickets often (but not always) have seat numbers on them. The degree to which people pay attention to those seat numbers varies tremendously. As far as I know, customers don't request seat numbers, they are just assigned automatically, though I guess if you buy two tickets you normally end up with side-by-side seats.

I sympathize about the motion sickness. It was a big problem for me when I was younger, and I once felt quite bad on a bus in the Swiss Alps.

I sat in front of the bus and don't remember the drive being that windy (compared to this one really tight switchback road in Montenegro up into the mountains), but I may not be remembering everything. Don't recall whether seats were reserved...but we did get the upfront seats because I really like to look out the front window. Just curious...why does someone get motion sickness on a bus but not a car? Is it a psychological control thing (i.e. cannot control the bus) or something about the way someone else drives? Good luck with finding your way to Dubrovnik.

Well it is easier to stop and get out and puke if one is in a car.

Vision is a major component of motion sickness, so being able to look forward at the horizon is often a lot better than watching things whiz by out the side window. I think it's related to the eyes' needing to re-focus over and over again, but I'm not sure. In any case, I find closing my eyes helpful when conditions get dicey.

Another difference can be speed. As someone else mentioned, being in a vehicle that's constantly speeding up and slowing down as it goes around curves sometimes causes me problems. Buses trying to stay on schedule may be more likely to do that than passenger cars.