Of the Android pros you'd like to consider are native support for any wired/wireless keyboards, mouse, or almost anythung out of the box and abilitu to add an external memory card.
Connecting a mouse will instantly show a coursor on the screen with full functionality of its components, same goes for keyboard, and capacity could reach up to 128GB (depending on which device you end up buying).
The Nexus 10 is best for software support but its hardware is arguably outdated (doesn't affect much).
Samsung devices are best for hardware and the software is a little less than that of the Nexus line (they take much less time to release updates in general compared to others).
Asus is the favorite of many for its design but its generally slower to release updates.
Considering its for your father, I'd recommend an N10 for best out-of-the-box experience with upmost software support... but it has no external memory support which is somewhat a bummer for non price-concerned individuals like you.