While normally i am a big apple products hater, i got to say that the ipad is the most senior friendly internet tablet out there. There is some nice android tablets, but the ipad seems to be easier for most people to learn and get used to, unless of course they already got associated with an android based smartphone.
Definitely tablet though, either Android or Ipad, less concerns when it comes to virus and malware, and less troubles overall compared to a computer. I make a living fixing computers and over 80% of my customers are the 60 and up crowd. They try so hard to learn it to stay in contact with the younger family members but they struggle so much on a standard PC format. But usually on a tablet they can deal with it because they cant mess things up as badly or get into trouble as fast... LOL
Even a Kindle Fire is a good way to get them online, they can use email, web browse, read books and magazines and even newspapers in digital form... There is a lot of tablet options out there and they are all good.
Now in his case... Definitely get a tablet that has cellular data through his carrier, being that he moves between two locations makes it easier. If he ever gets stuck somewhere without good cellular data coverage he can still connect to WiFi as needed but most of the time he can just turn it on and go.
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1984 Honda ATC200ES "Big Red"
1982 ATC200E "Hondie"
1988 TRX300FW "Project Quad" Still in progress....