Just came from Best Buy. Samsung rep said when I get my note 4 upgrade right away. He says people who have had the note for months have had issues with Lollipop because the device they had has been running kit Kat so long. I dunno. I'm gonna upgrade it and run it for 7 days and take it back before 14 days if I have battery issues. I hope not cause I like this phone.
I'm cringing just reading what that GeekSquad rep said! If that guy really said that problems were caused because the phone ran KK for so long, then.....
I recommend that if your phone comes with Kitkat, you use it for a few days to see how you like the interface, battery life, responsiveness, and basically how it runs overall. After that, you can upgrade to Lollipop if you wish and then do a comparison of the two OS's. After you upgrade, be sure to enter "recovery mode" and wipe cache. If you don't do this, then you may experience some issues due to KK still in the system cache. Battery life problems have been attributed to people not wiping cache... at least in a lot of cases as noted in many threads. Lollipop, as an OS, does "appear" to run faster and possibly smoother than KK, also a few options are available in LP that are not in KK. However, the interface will change and unless you run KK first, you won't know what those changes are.
I know you're on Sprint, but I'm going to mention anyways that Verizon has pushed out an OTA that disallows reverting to previous OS's (OAF or KK). If your phone update includes this particular OTA, you will not be able to revert back to either OAF or KK. There is a "safe" LP upgrade posted on XDA using ODIN instead of OTA. It's for Verizon, and possibly ATT (not sure), so you'll have to search it out XDA to be sure. Again, I know you're on Sprint, and I don't know if reverting can even be done on Sprint, so this info is just for the general population.
I'm on VZW and still run KK. I have no problems at all with anything mentioned by people who run LP.
Good luck and enjoy your new phone!