My favorite low level weapon has to be the Swashbuckler's Pistol, due to its healing effect.
And my favorite weapon of all-time is.... **drum roll** .... Scalleywag's Pistol (How can you resist "Not In Your Face!" skill)
Runner-up (Only because it's hard to get and higher level than Scalleywag's): Scoundral's Pistol
The best weapon for low level has to be the Haymaker Pistol, though you couldn't get it without a code and it was only available for a short time. I was able to one shot most enemies. EXTREMELY Over-powered!