Which is faster depends on how the inputs are used. Suppose N1 as the nmos at the bottom of Nmos stack, and N2 on top of that and assume all the input arrives at the NAND at the same time.
When connect VDD to the input, there are two ways. One is connecting VDD to N1, and nother is connecting VDD to N2.
Comparing the former to the one in your answer, there is no speed difference,but the latter is faster than the one in your answer.
And connecting the input to both pins of NAND doubles the input capacitance, which makes the circuit switch slower.