I found this thread from a few months ago very helpful.

I used the pine 2 x 4 method and have been happy with it but was very careful when picking out the board. I went through most of the pallet of 16 footers at Home Base before finding one that was straight enough. The guy running the lumberyard was very helpful after I told him what it was I was going to use it for.

I think one major consideration is whether you are planning to build a few boats or just this one. Most plan on one but its kind of like your favorite potato chip....