I agree with Token's philosophy here. To ask a single antenna to work optimally over the frequency range of 100kHz to 30MHz is probably a bit optimistic. This is a 300:1 frequency (and wavelength) range; for an antenna to be the best possible choice from all types available at every frequency over this range is asking an awful lot. I have multiple antennas available for the portions of the spectrum which interest me the most; at ID time, being able to select from among them via a switch is a great tool to have in your toolbag.
Given your real estate size, I can't see how you can lose with a skyloop or possibly a rhombic to cover a big chunk of the spectrum. An alternate antenna could be used to fill in holes in coverage as you see fit, and if the two antennas overlap in coverage in a chunk of the spectrum, even better.
I have a 100x300 foot suburban lot, but right now I have no wire antennas up other than a small EWE; it's not the greatest antenna, but it is a very simple wideband alternate choice.
I acquired a Wellbrook a few months back and am satisfied with its performance. At LF, I have been able to log most of the NDBs others have posted here, as well as several others. I do not currently DX MW, and I can't comment on its performance there, but given the number of high power MW stations in Chicago, I would prefer a resonant loop here. The NRC AA Loop (Alt-Azimuth, 36" box loop) is the best antenna I have ever used for MW...
For shortwave, the performance of the Wellbrook seems quite good above around 8MHz; I have been able to get reasonably good copy of, for instance, the 27MHz Euro SSTVs and 19M Euro pirates here in Chicago. I think that an SML is a great choice for a general purpose antenna which can be used to complement another primary antenna. In my book, the single greatest advantage of a small loop is that one can move it around in a lot to site it away from neighbor's houses to minimize interference pickup, something which is a lot harder to do with a larger wire antenna. The choice of which one to buy is a matter of personal preference, and there are many reviews of both the loops offered by Wellbrook and Pixel. A couple of reviews which need to be read if you end up leaning that way are:
"Active Loops, Active Voltage Probe and Wire Antennas; A Statistical Review of the Performance of Six Antennas (Part I)" by Jack R. Smith K8ZOA, Clifton Laboratories
http://www.cliftonlaboratories.com/Documents/Loop%20vs%20Loop%20Final-Final.pdf"The Pixel Technologies RF PRO-1A and Wellbrook Communications ALA1530 Active Loop Antennas Compared" By Guy Atkins KE7MAV
http://www.wellbrook.uk.com/reviews/ALA1530-vs-RFPRO-1AReview.pdfMy listening is concentrated in the 90 meter to 43 meter range, and for this range my workhorse antenna is a small (20" square 4 turn) resonant loop which tunes from 2500 to 7500kHz. This is a high Q (around 240) unshielded tunable loop, and being unshielded, it is somewhat like having casual sex without protection. An unshielded loop does not offer the same degree of QRN protection as do the shielded loops mentioned above. When local noise here is low (and that's currently about 90% of the time) the resonant loop will almost always exhibit a better S/N ratio and lower minimum discernible signal than the Wellbrook in this frequency range. It is not unusual to be able to detect a carrier fading up on the resonant loop 10 or 15 minutes before I can detect it on the Wellbrook.
I hope this helps in some small way!