I travel alone and can't afford to fly or hire private car. Share taxis I've had too many hair raising wild rides with drivers of questionable safety, and I scare easy. So I use bus PP-SR and vv. Takes about 5.5 hours, with a stop on the way, and I found it comfortable enough if you take one of the better companies' buses--it's cheap enough that I usually buy 2 seats, one for me and one for my daypack. Also do the same between PP and Battambang, Battambang to SR, and to coast.

If I were you and you have time for it I would definitely recommend to go PHN to Battambang by bus then next day by river boat to SR. We did this back in 2010 (opposite way) and took us 11 hours but one of the most exciting experiences in Cambodia (in February = dry season). All the floating villages and fismermen in the middle of nowhere. You can also go by boat from PHN directly to SR but heard its way too much "comfortable" just for tourists..Cheers and enjoy your trip..