If you consider percentage increases, then (the current bugged version of) GWFS becomes more appealing.
With the Everburn Blade, you get a (15.33/13.5) = 14% damage increase due to GWFS. (I'm calculating assuming Str Mod of +4 and the bugged version). Without the additional d4 reroll, it's a 10% damage increase.
Assuming you'd be hit by an enemy attack 50% of the time (roughly corresponding to AC 15-16 at low-ish levels), having 1 additional AC means you'd only be hit 45% of the time. Thus, you'll be hit 10% less often with +1 AC.
These are comparable, although I haven't numerically estimated the value of being less likely to lose concentration.
