Replacing external wood shutters

Wig

I'd like some suggestions for what wood to use.

I am replacing a pair of exterior window shutters each one being 160cm x 50cm.

I don't have the time to make a proper framed unit. It will have to be a sheet of something cut to size. I intend to paint with undercoat and gloss. I got Dulux weathershield already.

As I see it I can go for any of these:

Hardwood Plywood 18 x 1220 x 2440mm £38

Marine as above £80

Structural Softwood Plywood CE2+ 18x1220x2440mm £35

OSB 1, 2 or 3 Board 18 x 1220 x 2440mm similar price £27 - £38


We can forget these:
I also looked how much a solid wood panel 19mmx1000x2300 Pine wood £154
Tulip wood £170


OSB might look a bit rubbish through the paint with the uneven surface. bit on the other and no-one is really going to notice.

Which sheeting material should I use?

Thanks