There are basically 2 types of Kettlebells, Regular and Competition. Competition kettlebells tend to be larger with a smaller and squarer handle. The size of the competition kettlebell bell stays the same regardless of weight, this helps will consistency as you change weight. The handle is smaller to avoid sliding and lateral movement of the hand. Competition bells are great for personal usage and for high repetition but for the various changes of hand and holding positions not idea for double handed exercises.
Regular Kettlebells have a larger domed handle and the overall size of the bell increases with the weight. The larger handle will allow moderate lateral movement but the trade off is that you can use 2 hands and also hold the bell by the horns (sides of the handle) for lots of beginner exercises. I use regular bells whenever possible for my kettlebell workout classes, and if there is mixture of the two types, clients always opt for the regular ones first.
When buying your kettlebells make sure that the handle is not too over-sized and conversely not too small. The bell should sit comfortably in the racked position on the forearm. Look for consistency in the curves of the bell, sharp angles out of the body of the bell will cause wrist problems as will an overly rounded body. Cast iron are the only bell worth considering, avoid cheap vinyl options. Finally, bells with a flat rubber sole should also be avoided. Go for cast iron all over and nothing more. I use different coloured cast iron bells for my classes and the clients love them. They will also last you practically forever.
One final note on the handle. If you start to get serious calluses from certain exercises then I recommend using some sandpaper to smooth out the handle. A nice smooth handle will change the game when it comes to performing lots of Snatches, Cleans or High Pulls.
To see more posts about basics kettlebells workouts, go here.