I will be replacing a floating dock and have been trying to decide the same thing. Going from a galvanzed steel to aluminum floating dock. Can get aluminum, Trex, or ironwood decking at the same cost. I prefer the no maintenance aluminum decking but it makes a hollow clanking sound when you walk on it. Neighbors have it and it is annoying. Trex has been on my back deck for five years. Does not get hot but does mildew and I have to clean it with decking cleaner twice a year for mildew.
Easy job though, just spray it on and rinse. Use stainless screws because painted steel, galvanized and deck mate will rust. Tried all three. The cleaner speeds the rusting process.
Another neighbors dock is ironwood. I had never heard of it but it looks like teak or maybe mahogany. No knots. Each board must be pre drilled for screws or it will split. Very nice looking but after 1 year my neighbor had to treat his. Bleach and treat to bring bach the color. 25 year life according to my dock builder. It is his choice of materials.
Hope this helps, I still can't decide!

Ipe is very nice stuff. Super hard and heavy. A naturally oiled wood like teak. Very expensive. An excellent choice.

I wouldn't do cedar because it's so soft. Pure heart wood would be harder, but the cost is not worth it.

The newer plastics that are out are nice. They won't warp, are mold and mildew resistant. They also cost more than green treated. Products like Trex can be bent into complex curves. Of course the properties that allow them to be bent also means the product is rather weak. Pick up a 16' 2x6 and the ends will touch the ground. Your span rating with Trex is limited to 16". Something to consider.

I presume that you are not going to pull the pier unless ordered to. For your structure you'll want to use MARINE treated pilings. So long as you don't want to tie the Formula up to it, you'd want to use 4" posts. This is something the local lumber yard will have to order. The regular green treated ground contact wood that is in stock won't last in a marine enviroment. Sharpen the post with a hatchet and make up a pile cap that you can beat on. A piece of pipe with a 1/4" plate welded to the end works well. Now get out there in your row boat and start beating on it! Take marine pressure treated 2x4's and put one on each side of the pile so they cross and form a X. This will brace the piles against the boat. Try to keep the angles at a 45. The one end will be below the water line. At the end of the pier, turn the bracing so it runs parallel to the pier. Now put 2x8 standard treated headers (horizontal) for the deck to rest on. If you want to use a plastic decking you will need to run some joists (stringers). The material will proably require 16" spacing. This will give you 3 stingers for a 4' wide pier. If you go with a 2x8 you can span around 8'. Get some Simpson LUS26 hangers and face SCREW them to the headers. Drop in the joists and the pier is now ready for for your choice of deck.

Usually we just set the piles at a 5 foot spacing and then laid 2x12 planks across a 2x4 header.

just had a new dock built last year. light weight concrete
called cool crete 2 x 2 size about 20 pounds each. Not
hot no maint. ever. Got tired of fighting the wood.

A lot of the LOTO docks are concrete decked. I would say Trex or concrete

I would give CorrectDeck a look. Its what I chose for my deck at home, and I don't think I will ever use any kind of wood again.

25 year warranty, looks JUST like wood it has a great embossed grain, and comes in 4 colors and its manufactured in Maine.

http://www.correctdeck.com

Jon, mahogony is your only choice it will always look great and no splinters, and very little mant.

If Your Only Preference is Wood...
 

Definately go with the Ipe. It is incredibly beautiful. It is a south american hardwood that will look and last for 40-50 years. Zero maintainence forever. It is so durable, that it was the material chosen to redeck the New Jersey boardwalk a couple of years ago. Choose a good carpenter who appreciates finish carpentry, as it will look better than the furniture in your house! It wears out carbide saw blades, countersink bits, drill bits, etc...at an alarming rate. You can nail it with stainless nails, but would recommend #10 x 3" square socket drive counter-sunk head stainless deck screws. You might as well use the screws, because you have to pre-drill for either anyway! If you go with regular pressure-treat lumber, I would highly recommend a surface sealer/protectant by the name of "Wood Rx", in the natural color, that they offer. Incredible stuff! Blows the doors off the usual Home Depot/Lowe's deck stains. It runs about $100.00/5 gallon bucket. Look it up on line to find a source locally.Ed;)

Hey old buddy, pressure treated is the way to go.

Don't you need a boat to need a dock? :D :D

Plastic like trex is great but you need to have additional support as compared to wood. Wood is usually framed every twenty four inches and in some cases thirty inches. The trex needs more crossmembers or will sag.