Walking through the grocery store, you'll see a lot of varieties when it comes to drinks. Bottled water, flavored water, juice, sports drinks, soda, diet soda, coffee, tea, etc., etc., etc. What's the best choice?
Water is by far the best choice to make. There are no calories and all you need to do is turn on the faucet to get it. And, of course, the body needs it. There is no need to spend a lot of money on bottled water or flavored water. While there is no health reason to avoid bottled water, there is the environmental impact of the plastic bottles. If you don't like the taste of your water, you can naturally flavor it with lemon, lime, mint, berries, etc. You'll find this tastes much better than any store-bought flavored water and you'll know it was made with natural ingredients. Best part is, you can have as much as you want and save the calories for your food.
Coffee and tea are also good options. Both are calorie free and have some health benefits if taken in moderation. Just be careful what you put into it - cream and sugar have calories and should be tracked.
Milk can be a good option, depending on your specific nutritional needs. And once again, it should be drank in moderation. It is relatively high in calories, so you definitely want to watch your consumption. It also gives the body the calcium that it needs. So, how much you drink is really dependent on how much calcium you get in from other areas of your diet. I personally like to look for brands that are hormone free, but that's a topic that deserves to be addressed on it's own.
Diet sodas and powdered drinks that are artificially sweetened have no calories. However, the long-term effects of artificial sweeteners on the body is mostly unknown. I try and avoid artificial anything as much as possible in my diet, so I stay away from these. I'll have the occasional diet soda when out, but other than that I stick to water. Moderation is the key.
Juice, like milk, has health benefits, but also should take into account your diet as a whole. Like the fruit, 100% fruit juices contain vitamins and minerals that the body needs. Anyone who has ever made their own orange juice knows that it takes several oranges to make one glass of orange juice. This means juice will be higher in calories and contain more sugars. You are much better off eating the whole fruit to get in the nutrients. Do I have to say it? Moderation!
Alcohol, when taken in moderation, can have health benefits as well and can be included in a healthy diet. The key words in that sentence are "when taken in moderation". Again, there are calories that need to be accounted for in each glass/can. Alcohol (specifically wine) is covered in more detail here.
Drinks containing sugars should be avoided. Sodas, sports drinks, powdered drinks, energy drinks, etc. have no place in a healthy diet. The only possible exception would be the use of sports drinks for athletes. And by athletes, I mean people who train vigorously for an hour or more per day. This is not the average person, so I leave it in the avoid category.