What is the fastest logic gate?
ECL is both the fastest logic family and has the simplest internal structure of modern logic families, but like other bipolar-only families it has a not insignificant power draw. It is also incompatible with other logic families due to its signal voltages.

If you're looking for a logic family for general use, my recommendation would be the 74LVC CMOS family. It takes a supply of 1.65V to 5.5V, and uses normal CMOS signaling levels. It comes as surface mount only, but provides flexibility in that it is possible to get devices with as few as a single gate in a SOT23-5 package.