It all depends on what you have in mind regarding its uses. A model with 2 wheels has its set of advantages. First of all, it can be used for storing wood in good conditions. A firewood carrier with wheels keeps the wood away from bugs and prevents rot and mold from taking over.
Simultaneously, a cart with 2 wheels occupies significantly less space than one that comes with 4 wheels. The convenience offered might be considered the number one reason for choosing such a cart for many people.
Still, you must bear in mind that a model with 4 wheels can carry a lot more. If you have a lot of work to do in the garden, or your kids want to hop into the wagon for a ride, you will find a 4-wheeler a better choice than a 2-wheeler. Either way, each type has its upsides and downsides, and you should weigh them carefully before making a decision.