I would say the sheet is more durable, but you would have to buy a hood as well. The onsie has a neckpiece included. The material is pretty good, but it's a lycra type material, so it's not going to be as sturdy has nylon.
It's an entirely different application. The Onesie is a full body stretchy sheet that will fit a wider variety of horses. The mesh sheets are much more size specific...and yes in general, mesh is more durable than lycra, but it totally depends on your fencing or enclosures.
PHT onesie
