The difference is rather unimportant, but technically:
Uniform laws, such as the Uniform Commercial Code, are drafted by the Uniform Law Commission/National Conference of Commissioners on Uniform State Law with the goal of persuading legislatures of many different jurisdictions to actually adopt it in order to achieve uniformity across jurisdictions.
Model laws, such as the Model Penal Code, are drafted by other organizations (often the American Law Institute) with the goal of supplying a basis for individual state action on important topics. Uniformity isn't as much of a goal with model laws.
REMEMBER: uniform and model laws do NOT have the force of law in any jurisdiction unless and until they are enacted by that state's legislature! Additionally, legislatures can and often do make changes to the uniform/model law before enacting.