I MUCH prefer gerbils, I've had both and I think hamsters are a bit more common and boring. Here's my reasons:
1. Gerbils bite far less than hamsters, in fact they very very rarely bite.
2. Hamsters sleep all day and are up at night, where as gerbils take short naps during the day and night, so they're always ready to play when you are!
3. Gerbils naturally adapted in the desert, so they produce very little waste, MUCH less waste than hamsters. This also means you only need to clean out a gerbil cage approx. once a month, whereas hamsters need to be cleaned out more.
4. They eat and drink less than hamsters. This along with point 3 will actually save you money.
5. Gerbils need to live in pairs or small groups, 2 gerbils living together form an incredible bond! But you must buy at least 2 - a single gerbil is a lonely gerbil, and a lonely gerbil generally has a shorter life expectancy. Most species of hamster are better off living along because they're more aggressive and more likely to fight than gerbils.
6. Gerbils love to burrow, they need a cage with a deep base (e.g. a gerbilarium or tank) so they can have lots of sawdust to burrow and play around, they're fascinating to watch, and they're so clever!
7. Last but not least, a hamsters life expectancy is around 2 years old. With good care gerbils live up to the age of 5. My two gerbils are 4 years old and still going strong :)
I went from having a russian dwarf hamster to having 2 amazing gerbils. Of course I loved my little hamster to bits, but having experienced both, I'd pick gerbils any day! For a cage try a "gerbilarium" they have a deep base for lots of sawdust so they can dig :) You can purchase wooden toys, but avoid plastic because gerbils chew it up FAST, but actually I found that my gerbils liked the free toys! They love nothing more than a toilet roll or kitchen roll tube, pretty much anything cardboard goes down great, in fact my gerbils seem to prefer the free cardboard toys than anything I've ever purchased them!