Callum WIlson - Prem Apps - 126. Goals - 41.
Josh King - Prem Apps - 161. Goals 48.
Whilst you're correct in that Wilson has a better goals per game record, he very rarely played every game of the season for whatever reason (form, various injuries). Josh King on the other hand also played from the wing and featured in over 30 games in each season except the last.
I think if you're relying on a player to play week in, week out King is the better choice.