Coway is RO Water, and possibly adds back minerals at last stage of filtration, depends on model of filter.

Cuckoo is not RO, seem similar to LG, whereby it retains the mineral content present in the water. (based on the website marketing wording, doesn't seem like cuckoo filter cartridge is adding additional minerals)

Based on my own comparison prior to purchasing LG, LG's closest competitor is Jiksoo (only the tankless model). And I do ask my friends / family which I recommend LG, to go check out Jiksoo and see if they like it better. Jiksoo main downside is the fixed design water outlet and non inverter compressor, design wise to me personally, LG is better with the ability to rotate the water spout 180 degrees.

The brands you listed above, from my own comparison most water purifiers are tankless only for the ambient and hot water, but for cold water, so far only LG and Jiksoo are completely tankless.

LG does have some downside too being tankless.

For hot water LG can dispense a maximum of 1l, and needs rest for 20 minutes before it can start dispensing hot water again.

Also max 85degC hot water is hot enough for beverage but for instant mee, it needs to be hotter. My old Seers 3 second boiler, can output 95degC which was better for instant noodles, anyhow we don't really use our dispenser for instant noodles, so its a good trade off for me.

Also, a 5 second full power heating in microwave, can get the water up to boiling temp as well. Anyhow it's a point to consider. Some dispenser do mention they can output 90degC but in actual fact the temp is closer to 85DegC.

For cold water, on LG I tested a max of 2l to 2.3l can be output at a temperature of 17degC (at this point, it drops to 1bar of coldness) and takes about 1hr to get back to 3 bar of cold level. At 3 bar, the output temp is about 6degC to 9degC as measured by my cooking thermometer.

Ambient water is unlimited, and there is setting to dispense continuously for 3 minutes.

If you need continuous supply of hot water of more than 1l at one go, possibly need to look elsewhere but for general use, so far after nearly 3 weeks, we are still happy with it and have since replaced our ageing Seers dispenser and undersink Aquaphor filter.

I can share with you the comparison chart if you want.

LG purifier and filter is also halal certified by JAKIM.

The features between WD518 & WD516 is almost the same. The only different are:
1. WD518 without a tray, if overflow will be on table top
2. WD518 the head unable to rotate 180°
3. WD518 new feature can increase the water volume every 10ml or 50ml and save as favorite.