A boat builder might spend $120 on a 4x8 sheet of Okoume plywood; a residential contractor might spend $12.75 on a 4x8 sheet of OSB. Both, oddly enough, can go the distance in the proper environments.
Obviously, true marine plywood is a pleasure to machine, assemble and finish. You can't go with it. If you don't want to spend a fortune on Okoume marine plywood, and you don't want the weight of Teak, then meranti Hydrotek is an excellent compromise of cost and performance.
With that said ... I don't use marine plywood unless I have to. Dagnam, that stuff gets expensive. Russian - not Chinese - Baltic Birch is made with an exterior glue and less than a handful of voids per sheet. It's the standard for teardrop construction, and many Baltic Birch shells have decades of use under their belt. It's great stuff.
Commodity ACX and BCX plywood is Exterior Exposure 1 rated and is an acceptable choice for a plywood shell. It should be very carefully finished, however, with attention paid to sealing all the edges. It's not particularly attractive, either. Many of those panels have Douglas Fir veneers, which will check if left exposed. Others have paper-thin Radiata Pine face veneers, some of which will disappear after only one sanding!
Some builders use cabinet-grade interior-only plywood for the shell. To me, this is a risk. Cabinet-grade plywood from a lumberyard usually has an MDF or particleboard core, which is COMPLETELY UNSUITABLE for exterior construction. Veneer-core interior plywood, unfortunately, is often at the cheap end of the spectrum ($40-$50 a 4x8 3/4 sheet). It's quite a shame, actually. Unless you're lucky enough to live in an area where it's easy to special-order plywood from big manufacturers like Roseburg and Columbia, the choices are often slim. Anyhow, back on track .... interior-grade panels work - until they don't. You don't get the forgiveness inherent in an exterior-grade plywood.
Since you plan to paint the exterior, I'd go with Baltic Birch or ACX plywood. You don't want the telegraphing of a B- or C-grade panel, and unless you like spending money, I can't imagine marine plywood will improve the build. Take your savings and splurge on a higher quality paint
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