Plywood

Pros

• Also plywood is much stronger, especially for shelves. ... I'd just use plywood which should be able to handle light shelves.
• You’ll love the finished product if you go with a veneered plywood like maple.
• Plywood would be superior to mdf by far, especially on shelves meant to vary a load.
• plywood is lighter when you're hauling it up.
• If you want it cheap, pine or plywood.

Cons

• You can also use plywood, but it tends to warp over time.
• Plywood prices are being hit by the global market instability and you can thank my country for the most recent instability.
• Plywood definitely looks nicer and should be much straighter out of the box, but im not sure the cost difference justifies it.
• Plywood will absorb moisture like a sponge and will rot and decay and you will not have a nice time.
• I think #2 is acceptable for the cabin. Will look nicer than plywood or OSB.