Is the RoG swift PG278Q still worth buying?

Hey,
That monitor allows for GSYNC so gaming is a lot smoother usually, however the tradeoff is that the TN panel isn't as good as an IPS panel.

I love my IPS panel, so I'd have to actually see that TN panel in person to see if it warrants the cost and visual loss to get the smoother gaming.

Of course you need a good NVidia graphics card to justify it as well. I'd probably want a GTX970 or better (otherwise I'd be considering spending the money on a new GPU and cheaper monitor... it gets complicated).

Other:
You can get an IPS panel for the same cost with Freesync (also 2560x1440, 144Hz). It's a better monitor, but requires a supported AMD card. I assume you have NVidia but thought I should mention it just in case. That panel and an RX-480 would be a nice combination.

So...

We can't really answer your question without knowing your HARDWARE, games played, and how important screen quality is, but YES it's a good monitor overall if SMOOTH GAMING is your main goal.

One of the monitors I've recommended to some people is the Dell U2515H. It's a 25", IPS panel with great Warranty. It's only 60Hz, no GSYNC/FREESYNC, but it's all about the pros and cons.