Tomatoes as a whole can be classified in two categories based on the way they grow: determinate and indeterminate.
Determinate varieties, sometimes known as "bush" varieties, tend to stop growing at a genetically determined height. This height can range from a few inches tall to 4 to 5 feet tall, depending on the variety. Plants grow to this pre-determined height and bear fruit.
Indeterminate tomatoes keep growing until frost or something else kills them. They are a true vine, and in places without a frost will grow to 50 to 100 feet long.
When choosing a tomato to grow in the AeroGarden, look for dwarf determinate varieties (for the AG3 or AG7) and smaller determinates for the AG Extra. Unless you are a bonsai master, indeterminate varieties should not be attempted in the AeroGarden, although AeroGardens are great for starting indeterminate varieties indoors, for transplant into the outdoor garden.
The AeroGarden Cherry Tomato (for any AeroGarden) and Mega Cherry Tomato (for the Extra) are determinate varieties that have been selected due to their appropriate sizes for growing in AeroGardens.