I assume you're staying w/ motorola, given your candidates.. and most likely Verizon. But since its a wide-open, opinion question, I'll mention that the best bang for your buck would be to go tmo [no contract] [[or a mvno of such like jump]] and get a nexus 5 off the play store [you're guaranteed the latest android build(s) and price is better than competive; manufacturer is lg though].
That being said, above post is correct. Maxx offers bigger screen and great battery life; Moto X offers customized colors [so make sure if you get a case/cover for protection, its clear].
Rob