Depends on how you send it.
I use Messenger on my Note 5 and send things back and forth between it and my iPhone 6 Plus with little issue. For larger files I use GMail. I also use Google Photo at times.
I have noticed a couple of things.
... check your defaults for sending - MMS may be set to a lower quality.
... when sending from an iPhone (especially email) watch the iPhone size settings
... UHD photos look great on a UHD screen. The iPhone screen is not UHD (Ultra High Definition).
... colors between the two devices are different..
... lastly, if the photo just looks bad, check the default settings on both ends. Sometimes it is the photographer :-$