Your Preference: Resolution or Fullness?

It's not an either or question to me. If it is full sounding but does not resolve harmonic and spacial information, this is a shortcoming. If it resolves spacial information and sounds say, lean or veers in that direction this is a shortcoming. We all hear things and value them to varying degrees. There are MANY other aspects to include besides the two you mention. Overall I want natural musical and spacial resolution and the low level information on the recording, natural timbre and tone neither overly rich but definitely not lean, natural dynamic contrasts. In other words, I want the music to sound convincing. The above items are ALL equally important for that to be realized IMHO. I find too much richness or fullness to become as fatiguing as leanness. It's all about balance and this is the hardest part.

Gotta do both pretty well and sound good overall. Lots of good affordable gear is capable of both.

The main keys to both together is often getting a good integration with room acoustics and an amp that is 100% up to the task of driving the speakers to the max. Power needed to do this with many modern speaker designs, especially at higher volume levels and with many modern "louder" recordings in particular is often underestimated.

After that is done well, the rest is more or less "fine tuning" the sound. Everything else will have an impact in all ways and no two combos are likely to sound exactly the same, so individual preferences come into play to a large extent, assuming gear is good quality in general.

I don't have to choose. I get both.

If I would choose only one, I choose fullness

I actually agree with the OP's premise - that it's almost always a trade off. More "warmth" in the upper bass ("fullness") tends to obscure resolution in the lower mids to some degree. I also agree with Viridian that tone trumps all.

In my main system, I employ traditional, dynamic speakers from Merlin - which maximize resolution at the expense of (a bit of) fullness/warmth, and Verity - which offer more fullness/warmth at the expense of (a touch of) resolution.

Some A'goners seem to find the Merlins too "lean", but it's rare that I have a problem with their tonal balance. On most material, they're great. Same with the Verity: It's very rare that I'd ever crave more resolution. Yet, side by side, each speaker does illustrate the other's strength and weakness.

Dipoles and omnis can skin the cat a different way. Purportedly, the lightweight drivers of a planar (I own Maggies, too) provide resolution, while the reflected energy provides a sense of fullness. If an omni (eg Ohm) is voiced a little lean, you get a similar effect; resolution fleshed out with reflected energy. Some might argue that the latter (reflected energy) ends up obscuring the former (high resolution direct signal), but IME, that's highly room and set-up dependent.

All three approaches have their appeal, but most often I end up trying to split the baby with the Ohms.

Just MHO.

Marty