Until we see big OEM's other than samsung using exynos, developer support will be more focused on snapdragon because they are widely used in other phones. There will likely be many top tier android devices from multiple OEM's using the Snapdragon 805 SOC. Samsung is still the only OEM of any size buying the exynos SOC.
My bet is firmly in the snapdragon side for the Note 4. This iteration will prove no different from the last generation and the generation before it. Exynos developer support has been poor at best. There were even a couple of posts where developer device maintainers have stopped developing for it in protest. AOSP for the Exynos note 3 was a slooooooow grind. CM and AOSP was available much much quicker for the snapdragon.
History: Treo 600, Treo 650, Treo 700, HTC Titan, HTC Diamond, Nexus One, SGS1 (Captivate), Samsung Infuse, Galaxy Note, ATT Galaxy Note 2, T-Mobile Galaxy Note 3
Tablets: Nexus 7 2013 LTE, 2x Nook HD CM11, Nook HD+ CM11, Samsung Galaxy Tab 2 LTE, Asus MeMo Pad FHD 10 LTE