byler47 :
Should I get a 1440p 144hz widescreen monitor or a 1080p 75hz ultrawide? My main purpose is gaming, specifically a lot of FPS.
I don't share your love of lots of FPS. I like sufficient to be smooth.
With a 144hz 1440p monitor there is no AMD card that can drive it. The closest would be a vega 64, but it would choke on most settings. The 1080ti, which is for the moment goofy expensive, would be your best bet
You also need to remember that in order to have smooth gaming without massive tearing you need the FPS to be at the same rate as the refresh rate of the monitor. So a 144hz 1440p monitor would need to be at 2560x1440 x 144 frames per second. That is a lot of data to push. A 2560x1080 low res 21:9 monitor has approx 40% few pixels per screen, also the 75hz refresh rate means that fps above 75fps is meaningless since they will be discarded. Put another way, It means if you hit say 100fps that only 75% of your frames will rendered and the images will be very jerky and seem to jump around.
Another issue with 21:9 is what Dunlop0078 pointed out. Most games don't fully support this resolution. Even the ones which mostly do will look very weird if there are cut scenes since the cut scenes will be in 16:9
Finally with 21:9... I just personally hate the monitors. They are all so short. I prefer a taller screen. I tried a 34" 21:9 (3440x1440) and did not like it at all.
I also tried a 28" 4k, and found it to be far too small a screen for 4k. I went with a 16:9 1440p screen. That is what I would recommend. The fastest video cards are Nvidia. If you can afford it, I would suggest a g-sync 1440p panel so that when your video card can't keep up with the refresh rate it will dynamically sync your refresh rate to your FPS to avoid tearing. G-sync adds around $200 to the total cost, but it works better than free-sync.