Definitely would have to be D.
I've only been on all-grain for a few batches now, but every AG batch has been noticably better than the extract and steeping grains beers I made... Could just be I'm gaining experience, or it could be that using AG, as opposed to pounds and pounds of extract makes better beer? (E.g. no "extract twang" that I and many others have noticed)
It's definitely cheaper as well - extract prices are ridiculous...
An lastly, and probably most importantly, you have a lot of control with AG. You can only buy extract in certain base-malts (pale, pils, maybe munich if you're lucky, etc.), but you can use any combination at all of base malts in AG. Further, many grains need to be mashed, as opposed to just 'steeped', to get to their maximum potential. If you are going to mash your specialty grains, you myswell mash the whole darn thing, IMO. Oh what else, mash temp determines body and fermentability of the beer - extract is only so fermentable and you can't change what the producer of the extract intended. With AG, you pick your mash temp to determine the body you want to achieve... Etc. etc. etc.
One more thing - if you do single infusion mash and batch sparge, it really isn't that much harder than your normal extract + steep day. A little bit of extra time, but nothing significant. I was taking about 3.5-4 hours to brew extract batches with steeping grains (steeping takes 30 mins in itself!) a while back - now I'll gladly sacrifice the 5 hours (yes, only an extra 60-90 minutes I've experienced) to brew AG beers...
I'm sure others will go on and on as well. This is not to say that you can't make very solid beers with extract and steeping grains, but AG is the way to go IMO... If the evidence of everyone eventually converting wasn't enough...
EDIT: Forgot one more important facet of it, at least for me. When brewing with extract, I kind of felt like I was just following a recipe book and just cooking up something that someone else took all the hard time to create (e.g. mashing grains to create the extract). With AG, you are starting with the most simple ingredient of beer, milling it, mashing it, etc. You feel much more accomplished when you complete, IMO... The smell of the grain when you are mashing, etc. You just can't beat it.