Self-contained or "sealed" liquid-cooling kits--preassembled and completely sealed, they start at around just $60--allow you reap the benefits of a simple water-cooling setup without having to deal with any of the messy particulars. You just need to attach a water block to your CPU and a radiator/fan combination to your case, and you're off to the races, with nary a drop of coolant to worry about. You may lose customization options if you use self-contained kits like Corsair's Hydro H-series or NZXT's Kraken-series coolers, but you also lose most of the headaches typically associated with do-it-yourself liquid cooling. Leakage is highly unlikely as long as you don't bend or twist the tubing at sharp, weird angles.
Installing a self-contained liquid-cooling kit is about on a par with the difficulty of installing an aftermarket cooler for your CPU. If you need to water-cool only your overclocked processor, a sealed liquid cooler is a compelling option. Stick to DIY loops if you want to liquid-cool more than the single component, however--or if you want the bling factor of clear tubes filled with colorful coolant. Most sealed coolers are opaque.
So, which is better? Air cooling or water cooling? The answer depends on your particular usage needs.
One size does not fit all when it comes to case cooling, but most people can get by with fans alone. It's easy, and it's cheap. If, on the other hand, you're an enthusiast who needs the best cooling possible for your flaming CPU and a gaggle of graphics cards, a DIY water-cooling setup is in your future. Finally, try a sealed liquid cooler if you're considering liquid cooling either to keep your overclocked processor chilled or simply to benefit from reduced system noise.