I'll work backwards:
The trait I dislike a lot is if a kayak teeters from side to side with initial stability. Usually this occurs when a hard chine boat is too wide and too long which means it is meant to carry more load than the person in the boat. Its basically riding too high and it goes from one side to the other and never settles in the water. If a hard chine boat is narrower, usually the boat sinks a bit deeper and the water holds along the sides more and stops that. It's also governed by the steepness of the "V" of the bottom. You usually don't get that with rounded hulls.

That is the one trait that I find very annoying.

I don't mind an easy turning boat as long as it has a skeg to stiffen it if I need it.

Lack of initial stability is not a trade for speed. (for me) I know racing boats are very low initial stability but for normal paddling I find that annoying. I don't want to be on-guard while paddling like early Nordkaps.

Lastly, boats with no thigh bracing. I have to have that and for me that's what makes a kayak a kayak and not a recreational boat.

We all want comfort, good looks and light weight. The light weight is not always easy to build or find and once you're in the water its not that important.

Here's an interesting fact. I worked with Impex at a few in-water events. If the paddler is comfortable (seat / back band) they will buy it. If they are uncomfortable, it could be the greatest boat in the world and they are not buying it. Very experienced kayakers will modify a boat but generally, comfort rules. The sale staff will change seats, adjust back bands and do anything to get that person comfortable in the boat.