IPS gaming monitors have better color, much brighter/fuller image, however their response time isn't quite as fast as a TN gaming panel, so some of the FPS playing pros will forgo IPS. IMO unless you play as a pro, then going IPS is far more worth it. I have both the TN and IPS 27" 144hz which came out first, and the 165hz Asus gsync panels, and the IPS one is far superior for gaming, but does cost more. In CSGO I notice no difference in terms of rates, between them, but ROG Swifts, and look virtually identical when turned off, yet the IPS model gives a far better image overall.
You CAN get the best of both worlds, size/performance, but it isn't cheap, Asus makes a 100hz 34" Gsync IPS but it's 1200$ usually.
Regarding 144hz, it does make a huge difference, and anyone who claims the eye can't see over 60fps anyway hasn't actually tried looking at a 60hz and 100+hz side by side. Yes, telling the 100hz, 144hz, and 165hz is hard to do, but anything over 100hz is a huge improvement over 60hz though. Gsync, YMMV, for me, it's the very last thing on the list I'd look for in a gaming monitor, 100+hz, IPS, and size would be priorities over having Gsync, but having it isn't awful or anything.
If you mostly game at 1080p Asus, Benq, and a couple others make great 24" 144hz units for less than three hundred bucks, but they aren't IPS.