Still hard to say. Depends on what you want out of the weapon. For example, it would be easier to suppress the HK91 than it would the SR9 (for legal reasons). The SR9's barrel has polygonal rifling instead of lands 'n grooves like (most of) the HK91s. The SR9's barrel is also slightly longer than that of the HK91. I suppose you could say the SR9 might command a slightly higher price because it has more steel on the end of it...
I like the SR9 because it looks cleaner without the flash hider. But that just my opinion.
From a collectors point of view I would think the SR9 would be a better investment, due to the fact that there are less of them around.
If you check GB you'll see that 91's are plentiful. But it's sort of rare to see an SR9. One pops up from time to time.
But like the others have stated Condition is a more important factor in determining the value of the gun.
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