I think PAL Express will be the first one to use the Q300s/400s in the tropics. The closest operators in the regime that come to mind would be Island Air (Hawaii) and Royal Jordanian.
Q300s/400s seem to be more popular in the N.American and European markets vs. the ATRs which are more popular in these areas.
ATRs seem more economical than the Q400 in terms of fuel burn as expressed in other threads and in other fora (no figures here though). Don't exactly know the relative numbers vs. the Q300. The Q400 is indeed a hot rod and some claim even way overpowered(don't they all use the same PW engines?).
However, we must consider the context and strategy being used here. The Q400's near jet speeds has been constantly marketed by Bombardier. Perhaps PAL 's strategy is to use them for the more the previous routes that used the 737-300s such as CEB-GES/ILO/DVO/PPS or MNL-LGP/VRC and the Q300s in the CEB-DIPOOG/OZC/CDO/ZAM/CATICLAN/TAC or MNL-BUSUANGA/CAUAYAN/SANFERNANDO/SUR routes. The Q300 would fly the <300nm routes while the Q400 would take the denser and longer routes.
Whether the economics of higher speeds and shorter flying time justifies the higher fuel burn for the Q400 another question. And yes, while it is important for smart, operational people to be involved in decisions, it is a fact of life that bean counters are still needed to crunch the numbers such as RPK, ASK and other mundane things like operational (fixed and variable) and financing costs.
In any case, turbo-prop prices are less regulated than they were before. Besides, airlines can always levy surcharges to their fuel costing and pass it to the consumer.
Truly exciting times...