What type of hamster you get depends mainly on your experiance with hamsters.
Here is a brief description of each of the hamster types kept as pets, to help you make you desicion:The Syrian Hamster
If you are a beginner to the hamster world, a Syrian hamster is highly recommended as it is large, slow, and in most cases easier to handle that the other types of hamster. Once tame, the Syrian has a friendly nature, and if the hamster is being bought for a younger child, the Syrian is the hamster to choose. Most Syrians are around 15-18cm in length, and live an average of 2-3 years. They come in many different colours, and can have either a short or long coat. If the hamster has a short coat, you will generally not need to groom it, whereas a long haired hamster will need dailey grooming to keep its coat free of tangles. This can be done using a soft bristled toothbrush (non-electric!!) Syrians can be prone to a stress related disease, Wet Tail, and it is vital that veterinary treatment is sought immediately if a hamster shows symptoms of Wet Tail.
Syrian hamsters are solitary, and so when they reach maturity at around 6-8 weeks they will need to be kept in their own cage for the rest of their lives. If kept with another hamster they will eventually fight till the death.
Note: A "Teddy Bear" or "Black Bear" hamster or similar is a term petshops use to describe a Syrian hamster, and so the rules of one per cage apply to them too.The Campbell's Russian Dwarf Hamster
Campells are smaller than their Syrian relatives, measuring around 7-10cm in length. They are active little hamsters, and even when tame may be nippy. These hamsters are sociable and it is recommended, though not vital, that they live in same sex pairs (to prevent breeding) in a large cage. In some cases though, Campells may become territorial and fight, which means you must be prepared to buy/make another cage to house one of the pair. They are able to squeeze through the bars of some hamster cages, and so if the cage you have chosen has bars, you must ensure that the bars are no further than 1cm apart.They also come in many colours, but are only short haired.
Campells are generally not recommended for children, due to their small size and fast movements. Campells can be prone to diabetes. The average lifespan of the Campbell's Russian Dwarf Hamster is 1½-2 years although they can live longer.The Winter White Russian Dwarf Hamster
The Winter White is very similar to their relative the Campells hamster. They are usually around 8-10cm in length, and have a tendency to turn white in the winter (hence the name Winter White).
These hamsters are sociable and it is recommended, though not vital, that they live in same sex pairs (to prevent breeding) in a large cage. In some cases though, Winter Whites may become territorial and fight, which means you must be prepared to buy/make another cage to house one of the pair. They are able to squeeze through the bars of some hamster cages, and so if the cage you have chosen has bars, you must ensure that the bars are no further than 1cm apart.
The average lifespan of the Winter White Russian Dwarf Hamster is 1½-2 years although they can live longer.The Roborovski Hamster
The Roborovski Hamster is the smallest of the hamster species kept as pets, being only around 4-5 cm in length. They are often refered to as "furry fish" as they are much more difficult to handle than the other species of hamster. This makes them unsuitable pets for people who want a pet they can hold and play with but are a excellant choice for those who prefer to watch them go about their daily activities - particularly when given a large and interesting environment to live in. Roborovski hamsters do however have a very good temperament and rarely nip. They can be kept in pairs or groups, but will have to be seperated if fights break out. Although being the smallest, the Roborovski is generally the longest living hamster, living approximatly is 3-3½ years - although they can live longer! They come in one colour, and have a short coat.
I hope I have helped! Why not ask in Hamster Posts and Questions if you still have any questions?