I've had both. I had never been keen on autos previously, but decided last year to give it a go with a tourer in Classic trim. The smoothness of the gear-change won me over - on any prior (admittedly limited) occasions I'd tried an auto, the gear change was always a bit jerky and created a sense of not quite being in full control of the car. The autobox in the 75 was definitely superior in that regard.
One of the plus points for me was that from time to time, I enjoyed planting my foot and feeling it surge on up to the national speed limit (ahem) without any other input from me. In addition, it was definitely an easier drive in congested conditions, so if that reflects your driving environment then it's definitely worth considering. However, most of the time I don't have to endure such conditions so the difference wasn't that significant for me.
What was more significant was that it was difficult to get 500 miles out of a tank of diesel - 480 or even 450 was more normal (this was a tourer, so probably slightly worse in that regard than a saloon). Considering that I usually get more than 600 from a tank in a manual saloon, and that the annual road tax was £100 more, the driving experience wasn't worth the extra ownership costs, so when I was facing a large enough bill to keep it on the road (nothing impossible, just too many things at once) I decided it was better to pass it on to someone who could do that work themselves and keep the car on the road while I turned my attention to another 75. Perhaps I might have found those costs easier to justify had it been a top-spec example ...
