http://www.eurogamer.net/articles/digitalfoundry-battlefield-4-next-gen-face-off
http://www.eurogamer.net/articles/digitalfoundry-call-of-duty-ghosts-next-gen-face-off
PS4 is substantially better on both (not my opinion ...read the articles)
AC4 hasn't been compared yet but simply from looking at full HD gifs you can notice the xbox one version looks much worse...the difference in anti aliasing is almost as bad as on ghosts,
here's a snippet from Kotaku's comparisons if you want more than just Digital foundry's opinion
third-party games like Assassin’s Creed IV, Battlefield 4 and Call of Duty: Ghosts all look better on PS4 than their Xbox One counterparts, some — ACIV and Ghosts in particular — considerably so.
taken from http://www.kotaku.com.au/2013/11/ps4-vs-xbox-one-the-comparison-we-had-to-make/