[T-Mobile Galaxy Note 4 Q&A, Help & Troubleshooting] iunlock:
Well...here's my take on it....

Screen Resolution:

SAME Quad HD 2560x1440, BUT

5.7 inch, 515ppi Super AMOLED on the Note 4,

5.96 inch, 493ppi iPS on the Nexus 6. (Thanks to LG)

Processor and GPU:

SAME quad-core Qualcomm Snapdragon 805 at 2.7GHz w/ Adreno 420 GPU

Memory (RAM):

SAME 3GB RAM LPDDR3

Memory (Internal):

SAME 32GB & 64GB (N4 TBA)

This is where things start to tip strongly to the Note 4: [Highlights in RED = More/Better]

* As a photographer myself I know megapixels don't mean everything. BUT the sensor in the Note 4 is pretty awesome and with an aperture of f1.9, it has an edge over the Nexus 6. Let alone the extra megapixels. I have a feeling these two will be the top shooters in its class.

Camera (FRONT):

Note 4 @ 3.7 megapixels (f1.9) w/ 120 degree wide angle selfies + shoots 1080p video

Nexus 6 @ 2 megapixels w/ no wide angle + shoots only 720p video

Camera (REAR):

Note 4 @ 16 megapixels w/ OiS and 1/2.6" sensor. (Better for low light shooting)

+ 1080p Video @ 60 FPS

+ 4K UHD Video @ 30 FPS

Nexus 6 @ 13 megapixels w/ OiS and 1/3.06: sensor.

- 1080p Video @ 30 FPS

- [Edit] It does shoot 4K @ 30 FPS

Expandable Memory:

Note 4 = YES to 128GB

Nexus 6 = NOPE

Multi-Tasking Goodies w/ S-Pen:

Note 4 = YES

Nexus 6 = NO

Overall Size: (Personal preference.)

Note 4 (6.04 x 3.09 x 0.33 inches)

Nexus 6 (6.27 x 3.27 x 0.40 inches) [Taller, wider and thicker]

Weight: (Personal preference.)

Note 4 (6.21 oz)

Nexus 6 (6.49 oz)

Battery:

SAME @ 3220mAh, BUT

Removable in the Note 4

Stuck in the Nexus 6

Speakers:

Note 4's now on the back cover. (Hmmm....I liked it on the Note 3. This seems like a S5 carry over.)

Nexus 6 w/ Dual front facing speakers.

Design Language: (Personal preference, BUT practicality comes into play here.)

Note 4 really nailed it this time with the aluminum/magnesium frame and the back is nice and grippy.

Nexus 6 = HTC One meets Phone 6 meets Slippery Slide. WTH happened? Don't get me wrong, I think it's really clean, but it's a legitimate knock off of the HTC One. It's real interesting too how it followed the Note 4's design concept with the two little marks on the to end of the phone. (Antennas?) It's the little white stripes. The same ol' aluminum backing is a nightmare waiting to happen like the i6, HTC One and alike.

Price:

Worthless to talk about IMO, because if you're buying a phone at this level, price shouldn't even be in the conversation. You don't come to this league and gripe about pricing.

Software:

Absolutely worthless to talk about and to base any decisions on what it currently has. That's so freakishly stupid to me. Just because a device has Lollipop now doesn't mean that others won't get it LOL. It cracks me up on how some people get all hot and heavy over this stupid variable that doesn't matter! We're on XDA for crying out loud! What, you plan to keep you phone stock?! I mean geeezzz come on...If so you're in the wrong place.

Overall, I can't find ANY justification or reason to get a Nexus 6 over the Note 4. This will solely come down to personal preference in the design for the most part as...

....they both have the SAME CPU, RAM, Memory options, GPU and top of the line displays. At the end of the day if you factor in everything and add it all up the Note 4 obviously wins, however, either phone is a great choice to the average user. For power users who need expandable memory, the most vivid screen out on the market, upgradable battery, camera and software goodies....Note 4.