Is Grandpa coming along for the ride?
How is Grandpa going to feel about a somewhat more complicated/less convenient routing?
Because the best way to maximize your chance of F is for sure to go GEG-SFO-FRA on the A380... but SFO's weather regularly leading to ATC holds tends to make me nervous about tight connections. That's still how I'd look at it- while a groovy seat is indeed groovy, a busted connection can still ruin your day.