It is somewhat difficult to make clear conclusions about whether one room size has higher demand than another because the fact that one room size may usually disappear sooner than another does not necessarily mean it is in higher demand if the number of rooms in that size is low. However, based on what I have seen in reservation patterns in the last three years, one can make some reasonable conclusions for WDW resorts:
Studios are the highest demanded room sizes overall. They tend to disappear in the sequence of reservations before any other room sizes. At VGF they usually fill long before other sizes fill and there 2BRs and GVs are very often open even well beyond the 7 month window while studios are often gone before that window opens. Sometimes you see some exceptions, like BLT theme park and standard dedicated 2BRs and 1BRs may some times disappear before studios in those view categories, and some times studios are still open for AKV value when 1BRs are gone, but overall studios are no.1 in demand at all WDW resorts. However, VGF became the resort that demonstrates more than any other that Disney's substantial increases in the last four years in prices and points needed per night can take studios from being the ones of highest demand to the room size that is almost the only one in demand. During summer 2014, a usually low to moderate
DVC demand time, VGF dedicated 2BRs and GVs were often open even at 6 months out while the studios often disappeared before 7 months out and a similar pattern has occurred for many times in 2015. BLT has had some of that in that studios usually disappear there somewhat longer before 2BRs than at the remaining WDW resorts. At OKW, BCV, VWL and SSR studios tend to go first but usually not a very long time before 2BRs disappear. At BWV, stuidios including the dedicated usually disappear at the same time as the 2BRs (all of which are lockoffs).
2BRs are the second highest demanded rooms overall at WDW except for VGF where it is 1BRs. There are times when AKV value and BLT standard and TP view 1BRs go before 2BRs but that is only some times. On a few occassions I have seen BCV 1BRs go before all the 2BRs but that is a factor of the fewer number of potential 1BRs (note that the dedicated two queens 2BRs at BCV usually fill before any other rooms but that is mainly a factor of low numbers in relation to other rooms).
It is difficult to say whether 1BRs or GVs are the lowest in demand. GVs often disappear before 1BRs and more often before studios and 2BRs but that is likely more a factor of their lower numbers than higher demand. For example, the BWV GVs usually disappear before 7 months out year round because there are only seven but standard and Boardwalk view studios and 2BRs often disappear more quickly during the 11 month window during the high demand last quarter of the year. Similarly, the one or possibly two GVs at OKW in the Hospitality House booking category are often gone even before 11 months out but that is definitely caused by the small number of them. VGF GVs are often the last room size to go there. Elsewhere, GVs, despite low numbers, are often open at 7 months out between mid Jan and mid Sep, DVCs low to moderate demand season. As far as the room size which is open beyond all others, it is usually the 1BR with possible exceptions noted above but there are times when GVs are the last to go (e.g., for most of April 2015 right now, GVs are still available at three months out at BLT, OKW, VGF, SSR and AKV).
