Natural choice would be Beta, as this is where the juHqo' is located.

But well, it's the Alpha quadrant where most of the interesting action takes place, and most of the interesting locations are. Not all, but 90%.

I voted Alpha, but either Alpha or the Delta quadrants. Alpha for all of the reasons Hurga listed, and Delta because it was all something different from the usual Trek fare at the time and that makes it stand out a little more to me.

Alpha quadrant, because it had the most interesting variety of planets and species, and was where the federation was mostly located, otherwise, the beta quadrant, for romulan and klingon space, and the rest of federation space.

The delta quadrant also had some interesting planets and species too, like the borg, species 8472 (technically from fluidic space), nucleogenic lifeforms, voth, hirogen, vidiians and devore.

I said Alpha because that’s where the Federation is based and we know the most about it, but I also think the Delta Quadrant is pretty cool too with the Borg and stuff.