XL2720Z would be the better choice out of the three.
XL2430T is annoying to work with because the new options added to it caused a bunch of new bugs and there have been 5 (at least) firmwares updated for it, yet NO ONE has dumped a single one on the internet for users to self flash. Freaking amazing.
LG 24GM77 uses the EXACT Same panel as the VG248QE/XL2411Z/XL2420Z.
it's NOT a true 8 bit panel AT ALL.
it just does dithering differently than the other monitors (which is why people complained about banding on it).
Just for the record, the LG-24GM77 sitting on my table has an AUO M240HW01-V8 panel, the same as in other 144Hz 24" monitors (BenQ XL2411Z, Asus VG248QE,...). So it is just 6bit+FRC (see also Panelook).
Nevertheless, the LG-24GM77 uses a different signal processing as compared to the Asus VG248QE and probably also the BenQ. My guess is that LG relies on the dithering done by the panel electronics only, whereas Asus and BenQ do some additional dithering at the scaler level so as to minimize round-off noise caused by the pixel value processing (gamma, contrast scaling, RGB balance, etc.).