Need advice on an ND filter real quickly..

So I'm going to see Falling Water in early July and there are countless waterfalls there. I'm obviously bringing my camera and was interested in getting some seriously cool looking "spiderweb" waterfalls. (you know how when you LE, water can look like a thick spider web?) So, there are tons of options, .3, .this and point that...I'm confused. I'll likely be shooting with the 18-55 kit lens for the waterfalls or my 35mm 1.8G. Obviously these use 52mm threads. So I'm going to assume it'll be sunny 16 outside, but you know, I also want something that can be versatile as well. Not opposed to buying a stop up ring for when I buy some different threaded lenses.
Want to go Hoya or bust.
Any advice?

A circular polarizer will help slow down your shutter speed also, not as much as a ND, but it depends on how slow you want to go. All of the shots in my Fillmore Glen blog post are with a CP only. In direct sun you will need to go with a ND. You can also layer them for different effects. I really like how the CP cuts the glare off the water and reduces blown out highlights, it also shows more definition in the water flow.

I was going to suggest looking into a CP too. They can be used for tons of stuff I am always finding myself thinking dang it I need a CP to take care of that bland white sky I'm going to get with this picture...I thought that today when I shot the buffalo...