Which timber

[Cuppa]

That looks like Oregan. is the new bench going outside too? what is it for? how big is it going to be? These questions will really help in directing you down the right path mate.

I reckon it looks like untreated pine unless oregon can be bought with that 'milled' finish, (which I've never seen). Given the way it has rotted out, I would definitely use treated pine, but would also do what I could to sort the moisture problem before putting a new bench in.