PLS was developed by Samsung as a cheaper alternative to IPS, nowadays it's quite the same though (some say one or either is the best, whatever tbh) as far as I can see and read it depends on the monitor, e.g. PCB quality and what not. I'm using an overclocked QNIX so the colors aren't super 100% awesome crisp as they'd be on for example a "straight" IPS Overlord monitor (
http://overlordcomputer.com/), this is due to the overclocking though which distorts the colors a bit.
If you're a calibrating hero you can fiddle a lot with that.
Personally I think that IPS looks better, I've had both types of screens and even with calibrating and color profiles etc the IPS' just seems a tad more clear and better when overclocked imo.
Need the new beastly ASUS 27" 1440p 140hz.