I would suggest you take them if possible to a Metro store to hold and play with some of the phones.
While BIG screens are easier to input on And wanted more by us Techies, a lot of "normal" people think a phone with a near 5" screen is just Too Big for a carry all the time *phone* (I include myself in this group).
IMO, my 4.3" DX screen makes for a phone that is at the LARGEST end of my acceptable range. That the Motion was Smaller Than my DX was a solid selling point to me.
Dear God, I can't believe *I'd* be one to recommend the Avid but it may be the Perfect Compromise of larger screen and decent size carry phone for your parents. I agree with others that your parents are unlikely to notice the lack of techy wizardry in the Avid.
Nothing beats holding them all in your hands to be sure though.
Bruce in Ocala, FL