You need to answer two questions for deciding this: For how many people are you going to bake? and How often are you going to use your oven?
If the numbers are not high, you can go for small and compact ovens like these.
Suppose you bake more frequently and in higher quantities and also you have enough space in your kitchen or are planning to renovate your kitchen, you should go for built-in ovens or larger ovens like these.
If you plan to start a cake decorating business in the future, I would recommend going for larger or inbuilt ovens.
Also, there are microwave ovens available which have Oven features in a Microwave which is convenient for people who use both.