Hey, I own the PreSonus Eris E8 monitors and I must say, they are awesome!
I showed them to a soundengineer and a professional mastering-guy and they both said that the PreSonus sounds amazing and are better than a lot of monitors in higher pricescale. Both of em was impressed with the low frequencies, and said that they might have the best low freq in their pricerange.
I've owned the first gen rokit 6's for over 5 years. One of the speakers has a little bit of distortion / crackling, but I think that's due to some impact while moving. Otherwise, they have performed flawlessly over those 5 years. I have heard of others saying the low-mids can be a tad muddy sounding, but I think a lot of the times it comes down to the area they are being listened to in. They sound pretty good in my second bedroom which has some minimal acoustic treatment and no bass traps.
The best thing you can do is take some music you know really well (maybe some you've produced yourself) and listen to it on the speakers and see for yourself how they compare. You might be lucky to have your local music store have some in stock.
I have a pair of krk rokit 5 g2, I like them, and don't forget monitors aren't about good quality are about high fidelity, maybe in price/quality aspect you should go for Yamaha, if you wan't something top go for the adams a7, but I like my krk rokit 5 g2, I will keep them, they are more then enough for me.
I have no speakers to compare to, but I have the Eris E5 and am very happy. Very versatile in how they can be setup with the diff inputs, bass rolloffs etc. I went in mostly for the flat response too. My 2c.