Full range or subwoofer with bookshelfs for best bass at low to moderate volume?

Another factor: room + musical tastes. If I gravitated towards electronic, dub,etc the sub angle would be more attractive. However, no sub at all beats one that is improperly set up. So I went low risk, high reward.

Phasecorrect brings up an interesting point about the importance of set up as have others in this thread. In reading a review of the Elaq Debut  S12 EQ the reviewer came to the conclusion that it sounded better in his room than similar price subs that went lower and had more output, due to the built in EQ. So is it possible to spend a lot of time experimenting with placement and manual adjustments and equal the quality of sound of a sub with EQ? Other than the Elaq I have not seen other subs with EQ in my price range.

near full range speakers (40 hz or so) with a quality , higher powered amplifier .
i used to have psb tower speakers that played solid down to 40hz and a good NAD amp rated at 150 watts / channel. a powerful amp controls the speaker motion extremely well and has the power to create dynamic bursts even at low volume. the bass was spontaneous, tight and incredible and you could feel the impact from the excursions at really low volume.
the sign of a quality amp is to see if its rating goes up with a lower ohm spec, example 150 watts at 8 ohms, 200 watts at 4 ohms.  a good sign that the amp has a solid design and large enough transformers to have reserve power.  

Bookshelf + sub.
Because you will get the lowest hz, and because you can integrate it the way you want.
With a full range, boosting low frequecies is more challenging and you miss the 20s