I am growing both 4 and D. Initially I preferred D.
When I grow them, I get higher yields from the D than I do from the 4, I know, most say the opposite to be true, but in my case I got significantly more than the 4. Also its easier to keep the D happy, as I have some more trouble with the variegation on the 4 if I stray a bit from what she likes, and feed what I feed the D.
On the high, the D was more impressive and seemed to hit harder in the beginning, but just because it expresses more of the Indic side, while the 4 is more giggly and smiling, while still packing a big punch. When I haven't smoke her in a while, she affects mine and others balance just after smoking her, you don't feel like you are so high as the D, but in reality you are as if not even higher.
Taste is also more pleasant on the 4 and its grape/citrus/fruity where the D is just D taste.
I read that the original smokers called the 4 the "Reunion Pheno" , cause it was more like the original buds they purchased at the Greatful death concert.
Having played around with Rez's "D IBL" I can say that I have had way more pheno's expressing the Chem4 type smoke than the D. Also in the F2 and my own ChemD"IBL"xChemD. I am currently on my 2nd backX, looking forward to seeing what comes out of it.
I do have the Diesel #1, Headband, Original Diesel the Weasel edition of them, and I would call it a "ChemD light" with a bit fluffier buds and a bit more healthy.
When I say I prefer the 4 its not by a wide margin......And it can change periodically but when using the "empty jar" method LOL.....I always seem to finish the 4 faster every time . Ie. it must be the better one.
Have a good one
Satyr