Boots

2 attack should almost always provide less damage than 20 dex for a bowman or gunslinger I believe. Though, if you have a massive amount of dex already (2000 or so, for example), then the attack might provide more damage.

I'm feeling too lazy to go and crunch the numbers for which is better under which circumstances right now, but 20 dex should give more damage than 2 attack unless you're funded beyond belief.