Does the Ducky come in white?
Most folks like the feel of PBT. It has a texture like soft pumice, is a little denser than ABS (which affects the sound they make), and is more durable. PBT won't wear down to a shine nor will it yellow with age. So if you plan to keep the stock keycaps, go with the Ducky and its PBT keycaps.
Full disclosure: I am a big fan of the Filco. I have three (four if you count the one with MX blacks that I want to sell). They are top-notch boards. I don't care about the stock keycaps because I never keep the stock caps on any keyboard anyway. You really can't go wrong with a Filco, build quality-wise.
But those colorful PBT caps may be the deciding factor for you...