best way to regulate 3v3 from 25.2V (DC)
I think your best option would be to use a switch mode power supply. While they are more complex than using a linear regulator they can be made fairly small.

The problem with a simpler linear regulator is not just that they are inefficient, it is that the loss is turned into heat. At 25.2V the regulator would have to drop 21.9V to reach 3.3V. If the ESP-8266 draws around 170mA it will result in 3.723 Watts of heat.

You could manage this with a heat sink but this will take up space and radiate heat into your device.

A switch mode power supply will only produce small amounts of heat because it is far more efficient.