Re: Might jump ship from the S4...thoughts?
I have both. I have a 32GB S4 on ATT and it gets very little use. I also do not use all the features and over the years it just seems like the bloatware had gone over the top. I keep my S4 as a backup and it is getting very little face time. I do like the screen on the S4 and the SD card integration. I have learned to live with 32GB on the Nexus since I keep my music on Google Play Music and pictures on dropbox.
To be fair, I never had any performance issue on my S4, no lag as some others refer to but the Nexus 5 is a screamer for sure. If there is nothing that just bugs you about your S4, there is no real compelling reason to switch. The S4 camera is better as is the speaker. I might get a galaxy gear to use with my S4 to give it more face time and or when it gets 4.4 to use google wallet like I am now with my Moto X.
In short, I should like my S4 better than I do. Over the years I gave gone more to vanilla android due the overkill on features and bloatware on the Samsungs. In fact, this is the first time in a long time I have not used a Samsung as my main device...