Probably a switching regulator, though it depends on your load current.
If you drop 3.3V to 2.5V using an LDO, for example, it is going to dissipate (3.3-2.5)*Iload Watts of power. This means your efficiency is Pout/Pin=(2.5*Iload)/(3.3*Iload)=76%. Actually it's slightly worse due to the current consumption of the LDO itself. Meanwhile, switching regulators easily achieve >80% efficiency over most of their load current range.
Going from 2.5V to 1.8V your peak efficiency with an LDO is (1.8/2.5)=72% so again a switching regulator will have higher efficiency.
The Aussie Shield
: breakout all 28 pins to quick-connect terminals