Neither's better, but integrated models are neater as they're permanently installed and often have larger capacities. They're a good choice if you're having a new kitchen and have place to permanently put a microwave, although seriously consider a combi model that can act as a second oven, as this gives you more cooking options. Freestanding models are generally cheaper and come in a wider range of sizes. As they just plug in, they're easier to change if something goes wrong, and you can take them with you if you move house. Freestanding models are a good upgrade if you've got all of your integrated appliances already, or only have room for a single integrated oven.