My short, one line answer is: I suggest using professionally installed and certified Cat5e, you can't go wrong...
My long answer, with plenty of my own opinions (so take it for what it's worth...
Cat 5e is a widely accepted and supported cable. It is a modification of the Cat5 standard. However, everything I've read and understood from various vendors over the past few years indicates that Cat6 is a very nebulus and proprietary product. Cat 7 is even more proprietary, in terms of cable construction and terminating parts.
I *never* install regular Cat5 for data anymore. I use nothing but 350MHz Cat5e. 1000BaseT is widely supported across this cable, alot of vendor products can be interchanged easily, and the cable is a good price. If I really want to go all out, I would pick an enhanced Cat5e cable (say 400-600MHz). I would not pick any Cat6 or Cat7 product on the parket today.
Cat6 and Cat7 are (from what I understand) proprietary, and alot of industry pundits say that since the products are not interchangable, and vendor implementations and even the very construction vary widely. My bet is that current products and accessories won't last long. This makes me feel *very* uncomfortable using Cat6 or Cat7. I dread the thought of putting in a "weird" cabling system, only to have it unsupported after x-number of years, and way before the physical cable wears out.
In my view, the proliferation of Cat5e in the market means that the cabling will be supportable with plenty of replacement parts, from a variety of vendors for years to come. Contrast that with the performance benefits (which have proven negligible compared to Cat5e, anyway) from the Cat6 and Cat7 types of cabling and the very real threat of having obsolete or unsupportable cabling installed in your building long before the cable actually wears out.
A recent example of obsolete cabling: IBM Type 1 Token Ring cabling, which I have seen a particularly large installation completed in 1994, just before Token Ring over Cat5 came out. That installation alone is evidence enough for me to try my best to stick with widely available technologies, especially when considering labor-intensive installations such as building cabling.
The final point I want to make is that if you want to stay on the bleeding edge (say, with Fiber-to-the-Desktop, for example), you really should pull a hybrid (fiber and Cat5e together) to the desktop. This way, if your gamble on the fiber doesn't go the way you think, you can resort to more vanilla technology.
A current example of a gamble where I think I would pull Cat5e with: 3M's Volition passive optical cabling system. It looks neat, but I don't think it's going to last very long. Could this be another case of IBM Type 1 Cabling Syndrome?
