For much of my float flying experience, I always assumed that the EDO 3430 floats were THE ideal float for a working Cessna 185. In 1986, I was assigned a brand new (1985) Cessna 185 on PK 3500 C floats.....and I groaned. I groaned because I had previous experience flying a 185 on PK 3500A and B floats (straight and amphibious versions of the earlier PK floats), and those floats were water loving mothers, to say the least.
But, I wasn't buying the airplanes, I was being paid to fly them, so....for the next ten years, I flew that airplane and during the summers, I flew it on those PK 3500 C floats. I adapted. And it turned out the C and D model PKs are VERY different floats than their predecessors. After ten years, the engine in that airplane suffered a broken crankshaft in flight, and I parked the plane on a mountainside. It wasn't pretty.
So, my employer found a "loaner" 185 for me to fly till they could replace the airplane. The "loaner" was equipped with EDO 3430 floats....WAHOO!! (I thought).
My first few takeoffs at max weight were pretty disappointing as it turned out. The airplane just didn't perform as I'd remembered the EDO equipped airplanes. So, I went out with the plane and "relearned" what those floats want from the pilot to get them to perform.
At the end of the day, I found that the EDO equipped airplane would get airborne at almost exactly the same point (takeoff distance) as the PK equipped (3500C) airplane at max Gross Weight. I operated out of the Fairbanks, AK float pond, which is a narrow 5400 foot long water lane, with airplanes parked along it's entire length. So, it was easy to judge takeoff distance, based on "I got airborne right next to the blue and white Citabria" etc.
There are some even better floats out there nowadays, but either of these floats will work hard for you. That said, the PKs are going to demand more precise performance from the pilot. The secret to the PKs is they have a really narrow "sweet spot", and it takes some practice to hit that spot quickly so that the airplane accelerates well. The EDOs have a much larger sweet spot, and thus are if anything a little easier to fly well.
Both have very large lockers and flat tops. Both are good rough water floats, though the EDOs will pound more in wave action, due to their fluted bottoms. Repairs on the PKs are much easier, since everything on them is flat metal, whereas the EDOs have fluted bottoms. Parts are readily available for both, I believe. Aerocet offers PMA'd EDO rigging, as does, of course, EDO (now owned by Kenmore Air Harbor). PK is now PeeKay Floats, based in Maine, and owned by Alton Buchard, who is supportive and very knowledgeable.
I'd find out what a set of pork chops for those PKs are going to cost.
Otherwise, I'd look carefully for corrosion, and check for leaks, particularly on a set of floats that have been sitting outdoors for a long time, probably without anyone checking on their welfare. Easy to let water get in through the tops, then freeze and open up seams, etc. Do a leak check with a vacuum cleaner exhaust and soapy water before you get too far down the road to purchase.
I wouldn't be afraid of either set. They will both do a great job. As noted, the PK's will make you work a little harder at it, but their performance CAN equal that of the EDOs or at least so close you can't really tell the difference.
Finally, there are now arguably better floats out there for the C 185, but the price is going to be a lot higher, since these are newer floats. Both these floats you're talking about are HEAVY and LARGE floats, which impacts your legal useful load.
MTV