I have built Tamiya, Dragon, AFV, and Zvezda when it comes to 251's. Of those, I would pick Dragon over the rest, with AFV coming in second. Tamiya generally sacrifices a little detail for ease of assembly so you would definitely need AM. I just built the Zvezda and found it needlessly over-engineered in some spots and not so much in others. I have another but am in no rush to start it.
The AFV kits are fiddlier than Dragon, and the plastic can be a bit soft, but they look very good when done. Dragon issued most of its kits when they were still the king of the industry so they usually come with a bunch of stuff.
I have 14 SdKfz 251 kits; half are Dragon. 3 are AFV. The rest are Tamiya, Zvezda, and ICM (which I have not built yet, so can't comment on). I don't buy AM myself, but I don't find myself really needing anything, although you can certainly swap out tool clasps and stuff like that for that better scale effect. I would likely do it for any kit not made by Dragon or AFV, but YMMV.
While only the third vehicle is an Ausf D, I just wanted to give you a side-by-side of Tamiya, Dragon, AFV, and Zvezda to compare how they look completed:
TAMIYA

DRAGON

AFV

ZVEZDA
