Well I’m hardly an expert, but… assuming the sizes shown here are representative… It’s a tough call, but I’d have to go with Gun with a Sword.
First, we must remember how each of these weapons operates and their corresponding effectiveness. Balancing is absolutely key when it comes to swords, so any extra weight added onto it would throw the thing off by a fair amount in terms of accuracy (and most likely damage).
This means that any instance where a sword has a gun added to it would decrease the sword’s effectiveness. That’s a point away from Sword with a gun, sword with a sworded gun and gun with a gunded sword.
A = -1 B = 0
C = -1 D = -1
Next, we look to guns. In order for a gun to operate properly, the user needs to keep it steady and line up their shot to a vital organ, meaning it will work best when it’s not attached to a sword. A larger gun (all proportions remaining the same) will likely have a larger caliber bullet, but due to the increased mass will also fire the bullet at a slower speed. This means it will have overall less piercing power, but will cause more damage to what it hits. This point goes to Gun with a sword and gun with a gunded sword, since both of those have the biggest gun. However, Gunded Sword also has a second smaller gun that can do additional damage if it hits (we already took one point off for the lack of accuracy) so…
So in short: It comes down to either GWS or GWGS. Gun With a Sword is more reliable, but Gun with a Gunded Sword has high potential. I would put my money on Gun with a Sword.
Or maybe I’m taking this too seriously.