Initially, it can be mentioned that roller skates usually match your normal shoe size. It is also important to remember that roller skates have to go, like regular shoes.
Fitness and fitness skates are only available as inline roller skates and are good because they have comfort and roll well, even on longer trips. When choosing a fitness or fitness inliner roller skate, it's most important that they are comfortable with you. You can choose a slightly softer boot and thus compromise the responsiveness that comes with the rigid boot.
Freeskates are roller skates that can little more than the motion skate. Freeskates have a stiffer boots and medium wheels. This roller skate can be used for small drives and is more responsive. Control over this boot is great and an advantage if you want to drive fast through narrow places.
More specialized inliners:
Aggressive skates are very rigid, have small wheels and are compact. They are used for tricks on ramps or street obsticals.
Speed skates (race) here a low boot for better flexibility. The wheels are very large and the roller skate is designed to roll fast.
Hocky skates are rigid and have small wheels with a good bite on the ground. The roller skate is very responsive and can quickly change direction. A little different than other inliners, hocky roller skates only have laces as a closing mechanism.