The cabinets are resonance chambers that alter the frequency response, phase relationship, and audible reflections. Most of the reason for the $5 price point of the V3 Mix Libraries is not that they are only worth that, I would feel justified selling them for 5 times that much (as is done elsewhere) given the quality and quantity of sounds available in each package, but that I expect people to endure some trial and error in finding what works for them. To this end, the same amount spent on V3 Mix libraries yields vastly more bang for the buck and diversity of possible tonalities. Textual descriptions, sound clips, and recommendations are for the most part generalizations that may be completely useless as they are the experience of person providing them which will differ in hands, guitars, amps, playback, application, and preference to anyone else. That said, briefly based on what is up now (or will be by tomorrow (Sunn)) in the commercial section:
Mesa cab is a very balanced, industry standard sound. Defined and middle of the road in the frequency spectrum. Recommended for pretty much anything, but is most used in hard rock and metal.
Engl cab has a comb filtered sound that people either love, or hate, not really a happy medium, but a unique and cool vibe. Mostly recommended for metal, but I know of some guys that love it as a cool Marshall rock alternative.
Diezel cab is like a less dull Marshall cab, a little saggy but crisp. Recommended for pretty much anything.
Bogner cab has a very woody, lively tonality to it. Recommended for pretty much anything.
Sunn cab has a much deeper internal distance to the back baffle, and has a lower resonance frequency (when you palm mute, you feel it further down in the bass region), and since it is front loaded, it is also up front and not muffled sounding in the midrange and high end. Djent paradise (think Veil of Maya's "The Common Man's Collapse" tone - Marc used an Emperor cab which is a replica of the vintage original Sunn 412S I have).
Hope this helps!