For someone who really only plays mmo's/rpg games what is the resolution to go with - 1440p or 4k?
Everything depends on money and if you're willing to spend it for the premium experience.
1440p is the sweet spot at the moment. 4k will require compromising on settings/framerate on even the best hardware.
Not worth going 4k yet imo. Requires some serious hardware and even then, you'll struggle to get the frame rate to utilize 120hz+ monitors.
Unless you're talking world of warcraft
1440p is definitely the sweet spot and the resolution that a big chunk of GPUs can consistently hit 60 frames-per-second for the most demanding titles. The jump to 4K is a huge one. Native 4K 60fps is limited to a handful of cards - basically the top end RTX offerings from NVIDIA. And like Vash... older games in 4K is a lot easier. And competitive stuff like Overwatch you can hit 4K with quite a few cards.
These days I've been looking at three different options. As you get bigger in size the more GPU power you are going to require, but a starting point would be something like
1440p 16:9 - 2060
1440p 21:9 - 2070
4K or 1440p 32:9 - 2080
This is where it comes down to cost. How much do you want to spend?
You may also want to consider vertical height, a lot of people consider this to be quite important. You need to compare the height of the monitor for its size vs ratio.
This site is good for trying to compare them what they look like. Display Wars
I'm thinking my next monitor will be a 34" 1440p 21:9, unless I find some piles of cash laying arounf then I will get a 49" 1440p 32:9.