Why NAND better than NOR

i) PMOS in NAND is in parallel while that in NOR is in series

ii) Parallel PMOS makes a stronger pull up network than serial PMOS

iii) Since hole mobility is lesser than electron mobility, NAND-based design is faster than that of NOR-based design (because of parallel PMOS)

iv) t_phl and t_plh (high to low, low to high times) are more symmetric in NAND than in NOR. t_plh of NOR is slower because of the series PMOS.