Wide Lens is better.
Razor Fang - An item to be held by a Pokémon. When the holder successfully inflicts damage, the target may also flinch. (10% Chance of Flinch)
Wide Lens - An item to be held by a Pokémon. It's a magnifying lens that slightly boosts the accuracy of moves by 10%.
Thunder Fang - 95% -> 99% with Wide Lens.
Crunch - 100% -> 100%.
Iron Tail - 75% -> +13% (10% of 75%) = 88% with Wide Lens.
Ice Fang - 95% -> 99% with Wide Lens.
I WOULD SUGGEST YOU TO GO FOR WIDE LENS BECAUSE 10% FLINCH IS NOT SO MUCH, ALSO WIDE LENS RAISES ACCUARY LIKE YOU SEE UP AND ACCUARY IS BETTER THAN 10% FLINCH!
Special Thanks to Dark_Breeder for correcting me, Wide Lens doesn't boost to 100%, the maximum is 99%.
Hope this helps!