I don’t rate Dulux particularly – their oil based paints take forever to dry and the opacity is poor even though the paint is thick and sticky. I have done a lot of decorating over the years. I used some Dulux highly durable washable matt paint recently. This was good stuff however.
The paint that I find is very good is Johnstones. It’s more of a trade paint, cheap but has excellent opacity. Also quick drying. Oil based Eggshell is touch dry in 3-4 hours at room temperature! Covers brilliantly and isn’t all thick and sticky. Conversely, Dulux and some other brands take 24hrs or more – useless if you need to get a job finished quickly.
On technique, use a narrower roller if your walls aren’t perfect. This saves uneveness of finish.
Washables are quite new. The first time I used them was 3 years ago and cost a fortune – £45 for 2,5l! Thankfully they are much cheaper now. The first coat is always patchy no matter how careful you are. You use a great deal more paint on the first coat going on to existing emulsion. The second coat goes for miles, but you get great opacity coverage. Magic stuff! Traditional emulsion is finished except for ceilings perhaps.