They are essentially 2 different phones for different uses..The Phablet (N3) is great if you are into multi-tasking and using your phone as your primary go to device...Iphone 5s gives you a better form factor, one handed usage and touch ID....I used the Note 3 for a few hours (borrowed it to check it out from a freind)..All i did with the larger screen was play games and watch youtube videos..I do all this with my Ipad at home so really do not need to carry a very large phablet on me all the time (as my primary in pocket device)..On the flip side i have co-workers who use the ***** out of their note 3's with multitasking (Watching youtube while working on their email for example) so for them going to a iphone 5s is a non starter..
Its horses for courses...The Iphone5S meets the sweet spot nicely for most smartphone users that are not looking at serious gaming or media on their phones (Most use their tablets or laptops for that)....The Iphone 6 will probably upsize close to 5" than to 4" and apple may perhaps even make a phablet one day but we are really dealing with two very different devices ..
I do not hate samsung, I love all devices from all makers and loved the time i got to play around with the note-3..Its a great device for those that will really use it to the max...I would not be multi-tasking or using the S pen to all the crazy stuff it can do from my device so for me the iphone 5s is perfect for my usage..So if you are un-decided between the 5s and the GN3 you probably should go for the former, for you'd know if you really need a phablet based on your device usage.