It's not the size of the enclosure that matters, but the system Q (referred to as Qtc) and system resonance (in a sealed enclosure, this is Fc). This considers the size of the enclosure, as well as the Qts, Vas, and Fs of the speaker. Generally speaking, a high Qtc system (usually a smaller enclosure) will have more ringing, less low frequency performance, lower efficiency, and have a larger hump in the upper frequency response. A low Qtc system (usually a larger enclosure) will have more low frequency output, higher efficiency, and an almost non-existent hump in the response curve. It should be noted, however, that these assumptions should always hold true in an anechoic chamber; once installed in a vehicle, the transfer function (the effect the environment has on response) is a very dominant factor.
For the reasons outlined above, most reviews actually lack a lot of validity. For example, people do "drop-in" tests and say that one sub was better than another. These create a false positive of sorts; that is, for one speaker it was a higher system Q than it was for the other. The only accurate way to truly test speakers against each other is ensuring the same system Q and using in an anechoic chamber. If transfer function can be minimized, you can still have fairly effective results as long as system Q is identical for each speaker being compared.
