I used to travel on the route in my student days on the south coast, in the last years of the ubiquitous Stagecoach Alexander Olympian. Once away from the built up area of Portsmouth there's some good fast running as far as Havant, then some nice open country interspersed with villages as far as Chi and again to Bognor. After that... it gets a bit suburban and ploddy. For a long time. If you're hoping to see some coastline vistas you're out of luck until you reach Worthing! Would agree with above posters about the importance of finding an upstairs seat to make the best of the view. The last I knew of the route, it was the Brighton-Arundel runs that get favoured for single decks most, along with some (but by no means all) of the Chichester-Brighton via Yaptons. The Portsmouth journeys were almost all double deck.
It's a nice trip to do from time to time, but eventually the novelty of a 4 hour bus journey vs. the West Coastway, for the sake of saving the cost of a coffee, wore away. I think the introduction of nationwide free bus travel for pensioners has seen a substantial increase in the route's ridership, unsurprising given the part of the country it is in, and that has slowed things down a fair old bit. Each timetable revision has seen a bit more time added to the through run.. I'm sure the Southsea-Brighton through run used to be just shy of four hours, now it is 4h20m.
I couldn't believe the PVR figure of 40 at first sight so I went and did some guesswork with the timetable. This is what I concluded looking at the Mon-Fri off peak:
4h20m each way x2bph on the Pompey-Brightons = 18 buses with a 10 min layover at each end.
3h02m each way x2bph for the Chichester-Brighton via Yapton = 13 buses, giving a 13 minute layover at each end.
2h22m each way x2bph for the Arundel-Brightons = 10 buses, allowing for an 8 minute layover at each end.
So that's 41 buses, presuming the shortest realistic layover times.. if the layovers are any longer to factor in delays accrued on a 51 mile route, that figure will be even higher. Blimey.
If I were to do it again, I think the 1755 ex-Brighton on a sunny summer's evening would be one to take - the last through trip to Portsmouth, getting into Southsea at 2123: 3 and a half hours of spirited running on a fairy lightly loaded vehicle. This was the bus of choice on my way home from staying with friends in Brighton, and howling back down the A27 towards Portsmouth at sunset with the Spinnaker on the horizon is an especially fond memory of mine.