Actually, it depends on the breed of hamsters, All dwarf breeds are known for being feisty. However Syrians( aka Teddy Bear) hamsters are pretty sweet and docile.
My fancy Russian dwarf Wuddin nips from time to time, however my two Syrians have never ever bitten and they even come up to door of their cages to greet me at night. They have to be the sweetest things ^^
And the way to a hammies heart is treats, Yogurt drops, sun flower seeds, peanuts, Pumpkin seeds, etc. Just go slow, and don't force yourself on the hammie.
Also, In my personal opinion Guinea Pigs have a lot of flaws and not as many plus's. A list of which being, Their food is very expensive, they smell very very badly(worse then anything i've ever smelt, ever.), because they smell badly you have to clean them out often. They can be loud, one of my boys nips really hard for some odd reason, piggies are often very skittish,there are no properly sized cages on the market(you have to make a c&c cage, they are very fragile and last but not least, they require salad every day.
On the plus side, they are cute and fun to hold.