To fully appreciate the diversity and wonderful characters of Pokemon, you must first understand their individual characteristics. All Pokemon types can fight in a number of ways. Some can use Swords or Staves, others can use other items (including Pokeball). And some Pokemon can attack using their bite or claw. Knowing these characteristics, you can see why there is such a diverse range of Pokemon types.
What is the biggest characteristic of every Pokemon type? That would be speed. Pokemon that move quickly can usually beat Pokemon that take their time. Speed also determines the effectiveness of certain Pokemon types, and the ability to hit hard (even on a miss) with great damage. This is the basis of every type Pokemon chart and is used to create a battle format in which trainers can choose which Pokemon to use.
The second characteristic is special features. A Pokemon type chart uses special features like abilities and megaphones to distinguish Pokemon. These features are added to every to create a unique identity for each creature. This is what the dual-type Pokemon means, because Pokemon may have two forms ('regular' Pokemon and dual-form Pokemon), and they can switch between those forms with a simple turn or just use their special move.
There are a few special moves unique to particular Pokemon types that make them especially formidable in battles. The first type chart uses a very neat feature called 'ability'. This feature combines an ability, a move, and a type into one move that are super effective against that specific type. Fireball is an example of this, as its base power is based on the ability of the Pokemon to heat up, and its special move involves using a fire element, which is very effective against Pokemon with fire weaknesses.
Another type chart uses a very interesting concept called a hybrid type. It compares two Pokemon types by using the weaknesses and strengths of both to determine which is the strongest Pokemon. For instance, it has been determined that Pokemon that can learn the move Dark Pulse can beat the legendary Pokemon Deoxys with ease. This makes it so that Deoxys is only the weakest Pokemon (in terms of how many moves it can master). On the other hand, the two known hybrid species of the Pokemon world are arceus and metagross. Arceus and metagross have similarities with each other, but each has a few strengths that set it apart from the other.
Finally, another type chart has been created for a group of Pokemon known as the Swords. Unlike the dual-type Pokemon, a Swords user gains special moves by equipping it with either a blade or pole arm. It is this type of Pokemon that is the most powerful in the anime, as the anime has created a character (Arceus) known as the prince of peace who has two blades on both his arms - each with a unique move. The pole arm of the swords user is its strongest form, while the blade arm is its weakest.
Now that you know all the background information on each of the two main Pokemon types, you should be able to figure out what your personal favorites are. While the battle system may not seem that important, it can make or break your experience. This is especially true if you have chosen a particular team or if you want to use a certain in a battle. One of my personal favorites is Registy. Its cute appearance and highly effective moveset make it a great choice for a starter. Plus, its ability to learn more than two types of Pokemon and ability to block paralysis makes it a great to have in a tournament.