They are both great IPS monitors, so you can't go wrong with any of them.
In my opinion: I've hears the Asus MX series have a fantastic brightness, you will probably not need to change that a lot! 80000000:1 vs 5000000:1
But also the Asus lacks on one additional HDMI port compared to the LG one.
Both of them have display port, so if your GPU has a display port then great.
A couple of good points to consider on the Asus:
Trace Free Technology: Should allow you to reduce any lags on the image (if any)
MHL Compatibility - Only if you have an Asus mobile device.Otherwise it is
pointless.
Don't be fooled by the 'Splendid' preset feature. This is just a preset you can use and you will tweak your monitor the way you want.But it is great because mine has a demo, so it will make half of the screen Splendid so you can see the difference. It is useful if you want to have a similar calibration.
Good points on the LG
VESA mounting- this will be useful if you want to mount it later, so you don't need to bother knowing that your monitor is compatible
I don't think the Asus supports VESA mounting.(the VN I have does, it is a 24' one)
4-Screen Split mode: Quite impressed to see that feature, I could make good use of it to configure Cisco routers
, for my ccna labs
I didn't know the LG has speakers built in too, but there you go, if you ever need them they will be there. on both, Asus or LG. Just enough for a NOT massive room. So if you don't want to use your amplifiers(if you already have) and want to stay quiet at night that's enough.I think they have the same power as my VN's speakers.
Additional HDMI: I think you will use it.
*Note that the LG also seems to have MHL to link smartphones, but again, you may need to use a compatible device.
This link may be useful:
http://www.anandtech.com/show/7288/asus-mx299q-monitor-review/5
My word: I wouldn't spend that money on them as I would prefer to spend that money on a monitor with a higher refresh rate.(120hz+)