I used one 3/4" Coosa on the inside and one 3/4" Joubert Okoume on the outside mainly because the Coosa doesn't hold a screw well and I wanted that. The Okoume was pretty expensive also. I was surprised how much lighter the Coosa was once both were cut and ready to install.

but a quality composite,such as penske/coosa board,is definatley a much better choice,than plywood...

Properly installed and protected, wood will last almost as long as composites. In most cases longer than you will own the boat or the next guy/gal.
The problem in lies with aftermarket installations of hardware and fittings, not everyone beds them properly, water gets into the wood and presto, over time you will be replacing the wood.
I like the strength to weight ratio of composite.
In replacing coring in decks, hatches, transoms, caps, in using wood, that weight can up up fast on a 20-23 footer. Composite is lighter, stronger and not as susceptible to water intrusion.
Downside of composites is cost and proper installation of fastenings.
For me, I use composites, but not everyone's budget can handle that.
OP