I'm not sure if it counts as a 'favorite' since I've only made two pairs of socks, but I recently knit a pair of socks using Berrocco comfort, which is a nylon/acrylic mix. The socks are comfortable, soft, and washing machine safe (which will be good for my grandmother). The yarn was soft and nice to work with, but a little splitty.
I haven't washed or worn the socks much yet though, so I have no idea how well it will hold up. The yarn was a suggestion from my LYS ladies.