For me, it varies by trip. In general, I prefer to book pre- and post-days through ABD just for the ease of it (definitely includes transportation and breakfast and not having to move rooms).
If it's seriously expensive, I'll check out the ABD hotel and see if I can book it on my own, as you will sometimes still get the transportation, although it's definitely not a given! For my ABD Rhone River cruise that never happened (COVID) I was arriving by train with
@Grifdog22 and his dear wife, who were also doing the ABD. They booked their pre-day via ABD and got transportation from the train station to the ABD hotel. I booked my pre-day at the ABD hotel on my own (a SIGNIFICANT saving) and ABD refused to transport me to the hotel. They KNEW I was arriving with people they were transporting, and going to the same hotel, but would not do it. The trip never happened, so I don't know if the driver would actually have picked up just them and left me standing there, but that was ABD's policy. They also would not include the transfer from the hotel to the ship, even though, again, it was from the same hotel to the ship. So you really HAVE to check with ABD! It seems to be a moving target!
And sometimes, especially if I'm spending more than 2 pre-days, I will book a more reasonable hotel on my own and just get the transport myself. Again, it depends on the destination, because if I don't speak the language, I'm WAY more likely to just cough up the money for the ABD hotel/transportation.
Sayhello