I'm not specifically looking for the best performing 240mm cooler, just best for my situation.
I'm currently running an i5 4670k on the stock cooler, in the cooler master storm scout 2 advanced case. I chose this case because I move my PC at least 3 times a week and the built in handle was a huge draw. I also wish to go for liquid cooling because of the movement factor, I've heard that heavier coolers like the hyper 212 and other heavier coolers put strain on the motherboard which I would like to avoid just to be on the safe side. I will not be over clocking any time soon and probably won't consider it for at least another year (or until a time when I can afford to replace the CPU if something were to happen). In order to install a rad, I need to remove the top panel which is a single 240mm cover. Given this I would rather fill the entire hole than save some money on a 120mm and stare at the hole all day.
Now the reason I want to replace the stock cooler is because of my ambient temps, right now in the winter they are great ranging from 40-70 F but in the summer it can be anywhere from 90-110 and higher. While playing BF3 in the summer I averaged 81c which for haswell is fine but I would be much more comfortable if I could drop 10+c.
Reasons for 240mm
1. Fill 240mm hole on top of case.
2. Less weight on the motherboard due to frequency of movement.
3. High ambient temps.
OC not a major factor.
I will note that the less I spend on the cooler, the more I can spend on games and I like games.