If you're looking at "Sansa models" then you're probably considering the e200 range.
I have an e270. It's a great little device. However, it's probably less intuitive than the iPod, so if you're dad's a techno-phobe, then I wouldn't recommend it.
Also, Sansa models all use flash memory, which currently means they max out at 8 gigabytes - a little smaller than what you are considering.
Another thing to consider if your dad is a photographer is the screen size. The Sansas only have 1.8 inch screens. I'm a bit of a photographer myself, and have a few hundred pics on my Sansa, but I don't look at them much because of the small screen size.
You're probably better off going for a Creative Zen or something like that - bigger screen, higher memory capacity
Im looking for a full sized mps3 player(Big memory-like30GB,20GB-minimum and basic photo and video viewing). He is a big photographer so the photo viewing is a must. Video isnt that necessary. Also I use Napster To Go so compatability with the service would be preferable. So far Ive looked at the following:
Creative Zen Vision M
Toshba Gigabeat S
and some Sansa models