Having got both BF4 and Cod: AW for Christmas on PS4, I would say go for BF4.
Both have pretty good graphics, but COD still feels like every other COD game, constant spawn->die->spawn->die->spawn->die. It's still fast paced, but still suffers from bad respawn positions (you respawn directly in front of people), and largely if you are spotted you are dead - very little you can do to survive.
BF4 you generally feel like you are contributing more, you spend more time alive between respawns (generally), and if you do die, generally if feels "fair", i.e. you weren't in cover.
Both have pretty good graphics, but COD still feels like every other COD game, constant spawn->die->spawn->die->spawn->die. It's still fast paced, but still suffers from bad respawn positions (you respawn directly in front of people), and largely if you are spotted you are dead - very little you can do to survive.
BF4 you generally feel like you are contributing more, you spend more time alive between respawns (generally), and if you do die, generally if feels "fair", i.e. you weren't in cover.