Had both. I prefer 5.4L over 460.
I never have issues with spark plugs on my 3 5.4L , 1 4.6L, and 1 6.8L.
Reason I pick 5.4L is reliable, quiet, Great power, and better gas.
460 it reliable but life expectancy for them only good for up 150K then need rebuilt. Gas mileage is terrible. Doesn't like rev high.
Had 2 F250 superdutys 2wd with 5.4L they average in city 16 mpg and tow like 7000 pound 13-14 mpg. Still have power to able pull if you compare to 5.8L. 5.8L just run out of steam.