I generally prefer 1920x1200 because I like the 16:10 aspect ratio better than the 16:9 aspect ratio which make the monitor look wider, but shorter. However, not many 1200p monitors are manufactured so prices can be a bit more expensive than 1080p monitors.
I have a 24" Asus VK246H 1080p monitor which I have not used in over a year. I use my two 1920x1200 monitors from NEC / Planar. Sadly, laptops (not sure about Macs) do not offer a 1200p resolution screen so I have to bite the bullet and simply buy one with a 1080p screen.
As for 1440p, it's nice, but could be a bit big; physically speaking. But at least not a big as 1600p resolution monitors. It suppose it can give you better immersion in games because higher resolution generally means higher details, but you will need a pretty powerful GPU (or two) to get good performance in games at that resolution. Of course you can always drop the resolution to 1080p when playing games.