Water Bottle vs. Water Crock

Water Bottle

Water bottles are pretty universal, and the most popular way of giving water to your rabbit. Water bottles come in tons of sizes, colors, and styles. They can be made out of either glass or plastic. 
My rabbits are used to drinking from ball-tip water bottles. They can adjust to a wire-tip bottle or crock, just make sure they are actually learning properly and drinking the water. Rabbits are fast learners. 
Water bottles have to be cleaned thoroughly once a week or so with a special pet water bottle brush. 
Water bottles keep the water clean and fresh. 

Water Crock (bowl)

Water crocks are commonly used in rabbitries with over twenty rabbits and that live in colder climates. It's easy to fill up a crock with water or toss it in the dishwasher to clean it. If the water freezes, you can just bang the thing on something and the ice pops right out.
Water bowls are often very small and need to be refilled several times a day. The rabbit can urinate in its water, defecate in it, or just plain spill it. 

In my opinion, the water bottle is the best choice just because it stays cleaner and lasts longer. 
No matter the method of providing water you use, the rabbit should have water constantly available.