After 3 of 4 pcs, an iPad. It has only ONE button. My Mom is 88 and uses it.
She never ever got the PCs and seemed bored even though she complained about WANTING to use it. The iPad she uses, but I caution that your Dad may use it but not for you want him to. Life is like that sometimes.
My 81 year old mother loves her Apple Macintosh desktop. The screen is big enough and clear enough that she and my 89 year old father an use it. My mother now wants the new iPhone. She can't text on her phone but thinks she can text and use the Internet if she gets an iPhone. She also wants to use Siri to dial her calls.
My mother uses her iPad all the time. Browsing, email, and an assortment of apps, including Angry Birds (after getting through all the levels, she goes back and plays again, trying for a perfect score...me, i get stuck and give up!). She's 80 and did have a PC before this, but seems to much prefer the iPad. My dad, 83 next month, has no computer background at all, but has been able to use the iPad. It really is pretty darn accessible for non computer types, poor vision, etc.