Certainly I pay attention to the lower berth guest capacity of the vessels we are interested in. Primarily to determine the passenger space ratio. But one has to be a little careful in simply looking at that ratio (Achieved by dividing the gross tonnage by the number of passengers--lower bed capacity including solo-occupancy cabins), as some of the newer and larger ships have cut back on overall cabin sizes, in order to make more inside space available for extra charge venues and shops (purpose being to keep guests out of their cabins and into the mall environment of the newer ships).
In addition, since gross tonnage is a measurement of usable inside space on these vessels it is also important to recognize that they have also cut back on outside public space in order to increase inside retail venue sizes. This in turn limits the amount of space available for open deck relaxation and viewing areas necessary during during sail-aways and such cruises as Alaska or Panama Canal type voyaging.
Beside the number of passengers, also important is the number of crew, as the passenger to crew ration is a big factor for us as well.
We largely prefer smaller vessels, however, these are becoming available almost exclusively in the domain of the all inclusive, luxury, or quasi-luxury cruise lines, think $$$. The 11 major mass market lines have all gravitated toward very large ships and the escalation of size is still ongoing and rampant.