This isn’t really a trick question, but it is one where you will rarely get an honest answer from the sales person in your favorite electronics store. Prices for HDMI cables vary widely. You can find cables that sell for less than $10 and will also find major name brands selling for more than $100.
The real difference between an $20 cable and a $100 cable is $80. Wire is wire and as long as the cable meets the HDMI high-speed standard (almost all do), there is no functional difference and there is no performance difference between the two. The $80 difference is simply profit.
When we look for an HDMI cable, we simply make sure that it is rated as a high-speed cable, the connector pins are gold-plated, the connectors look to be sturdy, and the cable is wrapped in shielding.
The high-speed standard means that the wire is the proper gauge for the length of the cable so that it can handle the bandwidth produced by the digital audio and video signals. Typically, the longer the cable, the larger the diameter of the wire. A short cable may contain 28 gauge wire, while a longer cable might use 22 gauge wire. With wire gauge, the smaller the number, the larger the wire. The larger the wire, the more signal bandwidth it can pass without degradation.
Gold-plated connector pins do not tarnish, which helps maintain a good electrical connection. Even a small amount of tarnish on a connector can easily degrade the signal.
The sturdiness of the connector is a no-brainer. If the connectors look to be made poorly, the connections inside should also be questioned. Any HDMI cable with poor quality connectors are probably bootleg or manufacturing seconds.
While some people do not think that shielding for DC signals is important, it is important for two reasons. First, shielding prevents interference from power supplies and nearby AC wiring. Interference, especially AC interference, degrades the DC signal. Second, the signal does not degrade as easily over a longer run when the wiring is shielded. Some cables are wrapped with aluminum foil to provide shielding, while others use braided copper wire. Either one will work. We have seen $100 cables from a major manufacturer that did not look like it contained any shielding.
Regardless of which type of cables that you buy, do not buy cable lengths longer than what you need and always keep HDMI cables at least six inches away from AC wiring. That should assure that the cleanest and strongest signals are reaching your home theater components.