What is the fastest 7400 series family? Is 74VHC faster than 74AHC?
Previous answer is not fully correct because there is some issue to consider first. First there is two-three key categories which define "faster then" regarding:


Propagation/delay of input signal known as Tpd that is usually marketed by manufacturers and vendors, and it is usually measuring smallest time delay of signal on lowest possible capacitance setup on defined (max operating) Voltage.If it state XX on 15pF or YY on 50pF then it is OK, but when they provide results from 5pF or less it is practically unusable info.
Signal rise and fall time Tr/Tf usually measured from 10-90% of Vi-Vo if much more usefully information that define real speed, but often you can not see that info.
For example faster are 74ABT, 74AC, 74F that have Tr/Tf in on 5V low as 1.3-1.7ns, and 74VHC is 2,3-3ns, 74AHC/LVC are even worse. 74AUC, AVC are near first group but on half of voltage (2-3.3V)
And then what is max working frequency of considered 74series device depend on its internal and external capacitance that determine max working range in MHz. For example VHC can go up to 210MHz, but AHC is limited to 150-160MHz, AC has max like 100..140MHz.


At the end considering better noise immunity, larger working frequency and higher Io current VHC is winner over AHC in 5V category. But it is not produced in C/PDIP.

p.s. VHC is originally Fairchild improvement over AC series.