I think people need to first relaise there are rules to this. The topic is based off of Avatar: The Last Air Bender serise which does have a finite amount you can do with each element. Some of the things stated in this thread have been grossley taken out of preportion. So here's a crash course:
1. You need spiritual energy, or chi, to bend elements. This is non-negotiable. You also need to consider that most people have trouble tapping into their chi, which does require a good deal of training to achieve. Think monestary of shao-lin monks. So that would be a good deal of your life dedicated to learning how to bend.
2. Less than 1% of the characters in Avatar know how to achieve complciated bending techniques like metal bending, blood bending, lightning bending, blue flames, etc etc. Think of it in terms of animes such as Naruto or Bleach. You have two factors that determine your capability to bend: the amount of chi you have and your dexterity (for lack of a better term) in manipulating it. Large amounts of chi are used to bend things like metal (because of the large disassosiation with earth) where as bloodbending requires someone to manipulate every molecule in a person's body at the same time on a microscopic level. To say that anyone in this thread would achieve such feats (especially since this is about everyday practical use) is very unlikely.
3. Every bending technique is tied into a style of martial arts: Earth-Hung Gar, Fire-Northern Shaolin, Water-Tai Chi, Air-Ba Gua. Obviously this means that each has a philosophy behind them. As best demonstrated in Ang's (the main character/Avatar/last air bender) training with Toph (Earth bender), Ang had a lot of difficulty bending earth simply because his mind couldn't buy into the philosophies of earth bending (standing your ground versus freedom of movement). Then there are the kata (movements) associated with each element of bending, which are used to make chi flow to the proper points. To say that you could simply create fire in the palm of your hand just doesn't work as you need to focus your chi through these kata. This, of course, does not include very minute bending techniques (such as boiling a cup of water). Essentially, you must believe the philosophies of each bending technique and know the proper kata to perform any major sort of bending, such as shooting fireballs, creating tidal waves, moving large amounts of earth and flying.
Taking these points into consideration, as well as the general topic of conversation, I would choose water. My choice begins with my love for the philosophies behind the bending: flexibilty and fluidity. The tendancy to redirect confrontation rather than create it is something I enjoy more than, say, air Bending which is to simply avoid it. I also live near oceans so the resource is plentiful where I live. I'm also prone to carrying around a water bottle and it has been shown that wtaer is easiest to gather when you already have some being bent. The practical uses are almost endless. I could water my flowers, I always have a CLEAN source of water to drink (as will anyone else with me), I can create a cool environment in the summer (I enjoy the cold), I can make sure any minor injury I sustain is clean of infections or poisons, I'll never need a jacket in the rain, I can put out fires, I can walk over large bodies of water, I could always have a food supply if near a river/stream/lake with fish in it to catch: the list is almost endless.
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