New Vegas seems to have more personality over fallout 3.
First there is the added variety of weapons and unique weapons that actually look different. There is also more than 3 cities and each one has a unique aspect to them, many were invaded by gangs, others trying to survive, some don't have a care in the world and a few others are just incredibly poor. NPCs have more unique voices it's very rare that you will find someone that has the same voice as someone else. Ghouls have more than one voice now, same with raiders, old people, generic males, generic females, anyone with a name and even robots! Oh and the added variety of creatures, now it's not just one sized animal anymore. There is mother and father animals protecting their babies. There is wild bullhorns that are territorial and will growl if you come near them but they won't attack you unless you stand there too long. In other words, animals have more animal-like characteristics and they aren't just trying to kill you now.
Poll