There is some vital information needed before a responsible suggestion can be made.
What is your Video Card? The higher the resolution (L*W) the more work the video card has to do to keep up. Currently you are using 720p (1280x720=921,600 pixels) so to upgrade to a 1920x1200 (2,304,000 pixels, 250% of your current pixel count) or 2560x1600 (4,096,00 pixels, 450% of current) will put MUCH more strain on your video card, and thus, will be devastating for performance if your card is running maxed out @ 720p.
The difference between 720p and the resolutions mentioned is pretty big. If you have the hardware to push it, higher resolutions do look much better. Think about the difference between SDTV (640x480=307,200 pixels) and your triple pixel count 720p, and you might get an idea of how higher resolutions make things look better.