I've had several different breeds of hamsters and they all have different personalities and needs. What type of hamster to get depends greatly on what type of personality, size and how many you want to keep at a time.
Syrian aka Teddy Bear Hamsters- They are the most popular of the hamster breeds and are the largest. They can get anywhere from 4-6 inches long and live anywhere from 2-4 years. They are nocturnal so they make good pets for night owls since they will sleep all day and only come out at night. They are also solitary animals, meaning after they are weaned around 10 weeks of age, they should be kept in a cage by themselves. Syrian hamsters have been known to fight to the death if kept in the same cage together. These hamsters come in a variety of colors and hair lengths.
Roborovski Hamsters- These are the smallest breed of hamster measuring only 2-2 1/2 inches long. While they are nocturnal they will also come out and play during the day when they are young because they have so much energy and are always running around, which makes them a lot of fun to watch. They are small, active and fast and don't like being handled all that much. They don't sit still to be petted so if you are looking for a lap hamster that you want to cuddle and pet, this is not the hamster for you. This hamster is mostly for watching and playing with in a very controlled environment. If you take this hamster out of its cage, you should do so in a room that has been completely hamster proofed and has no or very little furniture that the hamster can hide under or in because once they run, they are very hard to catch. They are social animals meaning you can keep them in pairs or if your cage is big enough, a group as long as they have been introduced at a young age and don't fight. These tiny hamsters have a life span of 3-4 years which is longer than most other hamsters. These hamsters are sandy brown with white stomachs.
Chinese Dwarf Hamsters- These hamsters are also known as striped hamsters because of the black stripe of fur down their spines. Some people say they should be kept as solitary animals but I've had 7 of these hamsters and kept all the males in one cage and females in another without any major problems. The two girls did fight a bit but no blood was shed so it wasn't bad fighting. I watched them all cuddle together, sleep together and eat together. So it depends on the hamsters as to whether they will be happy in a group setting or alone. They are mostly social with people but sometimes they can be bitey. I had one that bit me to matter what I did. They generally live to be around 2 years old and are about 4 inches long.
I've had all three of these breeds of hamster and like all of them. The Roborovski are hard to handle but fun to watch. The Chinese Dwarf hamsters are fun to handle but rarely settle down long enough to be petted or cuddled and the Syrian hamsters are bigger, more social, cuddly and are easier to handle. No matter what hamster you decide to get, they should have a large enough cage to burrow in, have a separate place to sleep, eat, potty and play. They should have a wheel, tubes and space pod to sleep in. Hamster cages are a lot of fun because you can get so many add ons for them including locking tubes, add on pods, tubes that let you hook more than one cage together and play areas. The more space you give your hamster, the happier they will be.