The 3 best waters in Platinum are Empoleon, Gyarados, and Floatzel. Compared to Golduck, all of them evolve earlier and have a higher attack stat. You should consider using Golduck only if you're sure you don't want to use any of those 3.
If you're sure you don't want to use any of those 3, then Golduck is a pretty good choice. You can catch Psyduck early, and its special attack is higher than most of the other early Pokemon. Another Pokemon that's almost as good as Golduck is Octillery. Its attack stats are slightly higher, and it can learn gunk shot, signal beam, and fire blast. However, Octillery comes later and is worse in its other stats. You can also teach surf to a HM slave Bibarel, so you can use physical waters like Gyarados, Floatzel, or maybe Azumarill.