Types of In-line Skates

Recreational (top pic)
  For leisurely rides in the park. Comfort and durability are what to look for with a sturdy frame and a soft or comfortable hard boot. They usually have 4 wheels with a size around 70-80 mm or a little higher.

Aggressive (second pic)
  Made for tricks, jumping, rails, or half pipes. These skates are very solid and sturdy. With smaller, hard wheels for better maneuverability and durability. No brakes.

Speed (third pic)
  Lighter than recreational or aggressive skates, they are designed for faster skating. They have longer frames and a fifth wheel for more stability and longer strides. They have larger wheels for greater speed. No brakes of course.

Hockey (bottom pic)
  Almost the same as hockey skates, they are very durable, and have leather uppers with lots of padding for protection. They usually lace-up and have smaller wheels for faster turning.
No brakes.

Women's
  Women need a wider front foot, a narrower heel, and a higher instep. They are also lower cut in the back for the calves.