honestly, trying to compare via photos or videos offers way to many variables to make a good conclusion not to mention the variables introduced from the differences between the panels themselves. the best way of comparing is to see them in person which i know is not always an option.
as far as sharpness is concerned you can look at the pixels per inch chart and use to make a comparison. obviously the more pixels in resolution you pack into a smaller size the sharper the image will be.
as far as quality, panel type also matters. an 8-bit ips is definitely a noticible difference from a tn panel. you might want to search this directory for my other posts on the matter as i've went into detail about this quite a few times before.
I believe all or at least the vast majority of 2560x1440 monitors use IPS panels. Similar to 2560x1600 resolution monitors in which all of them use IPS panels.
Generally speaking, as long as you are using a monitor at it's native (maximum) resolution, you will get the best quality out of the monitor. This excludes color accuracy, for most people they simply adjust the settings until the colors looks good for them. For people who demands high color accuracy, then a colorimeter is necessary which can cost anywhere between $99 - $600. In this case, the general rule is the more it costs, the better the color accuracy can be.
The primary concern when using a high resolution monitor is the degredation of video quality. The more a video is stretched to fill a screen the greater the degredation will be. This can be easily seen when viewing a DVD (720p) movie on a 1920x1080 resolution monitor. When watching DVD movie in a window at it's native resolution, the movie will be sharp. When scaled up to fill a 1920x1080 screen it will become blurry. The same can be said for a Blu-Ray movie. Watching it on a 1920x1080 means it will be sharp. Watching it on a 2560x1440 resolution monitor means it will look a little blurry.
If your concern is with games then as long as you play games at the monitor's native resolution, then the graphics will look sharp because the game engine is capable of rending graphics at various resolutions. The problem will be the graphic card. The higher the resolution you play the more powerful the graphic card must be if you want to maintain the same performance level at a lower resolution with a weaker card.