A Windows phone can be a great choice for seniors if eyesight is good. These are easiest to use of all smartphones, cheap, and with voice input irresistible, even though cheap.
That is true even though Windows on a traditional computer is hard to navigate. Nonetheless Windows on a Windows phone is the ultimate in simplicity.
I suggest Windows phones even though my personal preference would be an Android smartphone and for those using an iPad I would recommend an iPhone. (The latter are expensive.)
Windows phones are currently falling in popularity and therefore cheap, and that makes them appealing.
Long-term they may even replace other Windows devices, however. You just plug a phone into a display and keyboard and it becomes your Windows computer. That is already true with the Nokia Lumia 920 smartphone.
Windows smartphones are $50-100 and plans from $10 and up