I guess YMMV. I suggest the iPad, strongly.
I got my parents each an iPad as a gift, and it was life transforming, especially for my mom. She never got a hang of computers, even though she even tried to take some computer classes. The mouse, the overlapping windowing interface, dialogs that pop up... a constant source of frustration. Desktop OSes require so much knowledge to just do basic things: we who were raised with them take it for granted. But the iPad somehow made sense to her. She never stops thanking me for it! She emails every day, looks up things in Google, and has recently started to use Facebook (although she is very confused by the interface... heck, I'm a programmer and I can barely understand FB's interface...). We also use Skype a lot, and it works great! Though she often forgets that she needs to "see my name in green" to know that I'm actually have Skype open. She thinks of the whole device as "also a telephone" and still doesn't quite understand that an "app" has to be open.
Related: my mom had a Galaxy phone at the time, and of course couldn't make heads or tails of it. But, once she "understood" the iPad, she also understood that the iPhone is just a "small iPad", and got one for herself. I'm so proud of her. :) It's also really interesting for me to see how she is exploring this new world in pretty much the opposite direction of what I expected: tablet first, smartphone later. Also interesting, I thought she might find the iPad Mini better, because she carries her iPad around all the time. But she told me she saw one that a friend of hers had, and thought it was ridiculously small and pointless!
For the record, I'm the ... opposite of an Apple fanboi. I have a Nexus 10 tablet myself, rooted with CynaogenMod. I use Ubuntu exclusively for my desktop and traveling netbook. For my needs, those are definitely the better choices. But for my mom, I must concede that iOS is simply easier to use. Fewer menus, fewer options, and that's all good for someone who is confused by even one option. I've learned that my mom not only has different needs, but also views these technologies from an entirely different, and I would say fresher perspective than mine.
Trust me: get you dad an old iPad, it may change his life. You definitely don't need an iPad 2 in terms of power, although consider the iPad Air. I'm thinking of upgrading my mom to it, I think she might appreciate the lighter weight.
Also: I don't know how old your dad is and how his vision is, but also look into increasing the font sizes, and show him how to use the click-zoom feature. It's built into the iPad, and can definitely help older folks.