Following performance numbers alone, then Fractal Design's Kelvin S24 is our most capable cooler. Second was ID-Cooling's newly released Frostflow 240L, followed closely by Thermaltake's Water 3.0 Extreme.
Best budget performer is Raijintek's Triton that manages to outclass many higher-priced coolers with ease, while still looking damn cool in action.
The most silent is Coolermaster's Nepton 240M, which had gone out of its way to dampen and reduce noise. While it's the most silent out of the bunch, it's still far louder than most air-coolers used for reference.
Instead of talking about individual prices - a price / performance graph would do wonders. As it stands, all-in-one coolers are more expensive that most air-coolers, and by performance numbers alone, air-coolers offer more bang for the buck.
If you're interested in some added performance, but aren't willing to go the extra mile, then a large tower cooler should do the trick. However, if you want to go for liquid then there are several budget options available, such as Antec's H20 1250. Some, like Alphacool Eisberg and Raijintek are impressive looking and still offer some excellent performance for their price point.
On the other end is Fractal Design's Kelvin S24 - which is more expensive than most AIOs in its class, and the most expensive on this list. It's build suggests FD spared no expense in its design and construction, and while it can function as an AIO quite nicely - it's as expandable as a custom-loop kit.
There are plenty of liquid coolers to choose from, and depending on what you're looking for - there are at least a handful of choices available. Each user has different system requirements and needs. All performance, build quality, and even design need to be taken into account - because after all for some users, looks might be just as important as performance.
If thermal performance is the most important part, and cost doesn't matter, then Fractal Design's Kelvin S24 or ID Cooling's Frostflow 240L offer similar results, though S24 is slightly more capable.
If customizability is something you're after, and don't want a custom-loop, then Alphacool's Eisberg and S24 have expandability features at their disposal. Even Raijintek, Coolermaster Nepton and Deepcool's Captain have an option to refill the coolant at a later date, though opening their coupler voids warranty.
If silence is your thing, there are some decent performers in this bracket as well, such as Coolermaster's Nepton 240M, which is the most silent all-in-one, but still a lot louder than most air solutions out there.