Just a short question wheater you change the dynamic effort exercise after 3 weeks or is it all year round the same exercise?
If your doing it according to readings on Westside, then it depends.
Those new to the system are best off using the same exercise for DE, but changing up the type of wave. Like a 3 week lactic acid tolerance wave followed by a three week free weight wave (use around 10% more bar weight when using free weight), followed by a 3 week wave with bands. That's not to say there's anything wrong with sticking to the basic wave for multiple waves.
For those that are more advanced, they might change the exercise and/or amount/type of accommodating resistance for DE every week.
I abandoned "speed" work long ago. It was simply doing more harm than good. I know a lot of the WS crew don't do them anymore either. If you follow what Fred Hatfield did, prior to the invention of the Dynamic Method, he called it Compensatory Acceleration. That is, every rep should be completed with maximal speed, regardless of weight. Don't allow yourself to slow down near the top just because you are about to lock it out. "Nobody ever tried to lift a heavy weight slowly" is a quote from him that I always remember.