Which does the best job of cleaning ? SeaFoam or Mercury Quicklean , or should i use both , can you use to much ?

I've always used Seafoam bc everyone I know also uses it. 

I run the Mercury Quickclean, Quickcare and Stabilizer in my Mercury.  I use Seafoam for all my other small engines (lawnmower, weed whacker, etc...).  Since I started using the Merc products my motor runs great, I will continue to use.  Whichever you go with I'd use the recommended amount as directed on the product.

Can someone explain the benifits of seafoam. I still think of it as an old school engine detergent. 

Apologies for the hijack 

It's basically a fuel system "cleaner".  Breaks up gunk and carbon deposits.  It also acts as a fuel stabilizer.  I've used it a couple times when I'm too lazy to pull apart a carb that's been sitting too long.  It seems to do the trick pretty well.  Not sure it's much better than the other products on the market but I've had good success with it.

As stated above it is a fuel system cleaner but it also decarbs an engine, which is a big benefit for an outboard, especially a two stroke. There are several u tube videos that show the interior of an engine before and after using seafoam(with a camera thru the spark plug hole), it works. I don't know that it is any better than the Mercury product but I suspect for $6.50 at Walmart, it is cheaper(just a guess). I free pour when I mix in a gas can but I would suggest mixing by the directions if you are in doubt.

I always put some Seafoam along with Startron when I  need gas. Since starting this combo, my boat cranks and runs better. I even hear a difference in the sound of my motor, I really thinks it helps.

I use seafoam in everything.  Works great.  I didnt know Mercury had a similar product and thus have not tried it.