• When picking between a water bowl and bottle, you have to consider the problems of each one.
• Water bottles are good because you can fill the water all the way to the top and be able to see how much your hamster is drinking. The problems with them though are that they can get dirty more quickly, however it's not a lot. Some bottles can also break and either all the water rushes out of the bottle or the hamster isn't able to get any water out of it. 
• Water bowls are thought to be more hygienic and can be cleaned easier. But because you're giving your hamster a bowl of water there's always a chance that they may drown. It might seem silly, but especially with the smaller species there have been hamsters that have drowned in the water bowl. Another problem is that a hamster could knock the bowl over if it's not balanced properly, all the water would then be over the bedding. Hamsters don't deal well with dampness either and can develop colds. 
• Some owners provide their hamsters with both so it gives them more choice. I use a water bottle because I was worried about the bowl falling over or my hamster getting wet as they don't like dampness. 

*picture credit to omlet.us*