Hamsters are great, though not as great as gerbils. They tend to be messier, smellier, less friendly, etc. than gerbils (I totally love gerbils, though!) Basic care and space requirements are pretty much the same (you have to change gerbil cages less frequently, generally, as they are cleaner). Both gerbils and hamsters have been rather hit-or-miss on whether they like exercise wheels. Some do, some don't. Hamsters are generally more active than gerbils and less 'hang-out" kind of pets, more "play!" kind of pets. By which I mean setting up little mazes and climbing things and chewing things like for piggie floor time for the hammie versus cuddles and setting a gerbil on your shoulder with a snack. Hammies are absolutely hilarious with the cheek pouches, though- that I love. Gerbils tend to live longer, too- hammies live like 2-4 years, gerbils 3-5? Or something. Not a huge difference, I guess. My personal hammie lived to be like 4ish and my gerbils almost to 6. So...
It also depends a LOT on breed (species?) or hamster. The Syrians, in my experience, are nippier and even more hyper. The teddies are ususally more cuddly (though not as much as a gerbil). And of course- a lot depends on socialization. You can have horrible terrors and sweathearts just depending on that. I (sadly) don't have experience with rescue hamsters of gerbils- mine came from accidental breedings of friend's petstore pets (where have we heard that before?) So I don't know if they are easy to tame down once adults or not.
Like samoews said, though- usually hammies do best by themselves. Gerbils need buddies, as they are really social animals, hamsters are more solitary.
And personally- I hate those cages with tubes. They are horrors to clean. I like best a 10g with a wire topper. Then you can have the bedding in the bottom for them to fling all around and more space and ventilation in the top. I would give all the paper towel and toilet paper tubes to them and make the bedding deep so that they could burrow and make tunnels to their own specifications (added bonus they doubled as a chew-toy and were free). That seemed an ok amount of room for two gerbils (are there tank-toppers for 20 gallons? I don't know...) but probably wouldn't be enough for two hamsters (like boars- they need space so they won't fight). The wire ones I like, too- though getting a big enough one with high sides (for burrowing and to keep the spray of bedding down) is super tricky. I went through like 5 cages before I was satisfied... :sarcastic