I’m using an Asus VG275Q (27″, 1080p), exclusively as a retrogaming/OSSC monitor.
I’ll try to write down some pros and cons, hoping it can be of some help:
+ it’s a gaming monitor (1ms), and I can confirm it performs remarkably well with all my consoles (MD, Saturn, PS1, PS2, original XBOX, GameCube, GBA through Game Boy Interface…)
+ greatly versatile, both in terms of aspect ratio controls and mobility. It can be rotated 90° clockwise AND counterclockwise, which is especially useful with all those older SHMUPS that didn’t come with extensive display settings
+ picture quality and color fidelity (in sRGB mode, at least) are actually pretty good, in spite of it being a TN monitor
+ as a TN display, it grants perfect stability with interlaced sources, and doesn’t suffer from flicker retention like IPS’ tend to do
+ once again, due to its technology, backlight bleed and corners’ glow are pretty much non existent issues
+ it allows to save up to 4 different color profiles
+ it supports every OSSC video mode (except 480i Line3x)
– build quality isn’t the best (we’re talking about a 250/300-ish euros monitor, but I expected more nonetheless)
– scaling capabilities appear to be very limited. Scanlines only look great in Line2x mode, while in Line4x they are uneven and basically unusable: it’s not a problem, to me personally – as I love Line2x and I use it for everything – but I realize it could be a huge constraint for many others
– I assume due to the previous point, 480i passthrough is out of whack, unfortunately (stretched to fullscreen and blurry… A giant mess)
All that said, I’m not sure how well the Asus would fare with an XBOX One. If you want to use only one monitor for both retro and current gaming, a 1440p (or straight up 4K) solution could probably fit the bill better than a full HD one.