Which file should I keep, JPG or HEIC?

So to address the duplicates that are in my library, I should delete the jpeg image (using Photos) and keep the HEIC image?

Since your Mac is running High Sierra, the system can cope with HEIC images. I would keep the HEIC versions and delete the JPEGs, since the HEIC versions need only half the storage. Only, if you need to use third party external editors, hat cannot read HEIC images, I would keep the JPEGS.

Those show up as JPG files in Photos. When I connect my iPhone by USB and import into Photos, the same image comes in as a HEIC file. Which one should I keep in my Photos library in Mac OS?

The HEIC codec has a better compression and needs only half the storage of the JPEG version. If you do not use photo editing extensions or external editors, that cannot handle the HEIC format (like DxO Perspective, for example), it will be less trouble to keep the JPEG version. But if you are only using software , that has been updated to handle HEIC, go for the HEIC versions to save storage.

Is your iPhone running iOS 11? Then you can set the settings on the iPhone to use HEIC consistently and not to convert the HEIC files to JPEG, when importing by USB, see Using HEIF or HEVC media on Apple devices - Apple Support

Both - you can never delete or change anything from the Photos library - there are no user serviceable parts in it

Are you using iCloud Photo Library on the iPhone? if you are then stop manually importing - that does not work everything is syncs by ICPL and importing again will only make things a mess

LN

OP states they are using Yosemite which does not have HEIC support

MacBook Pro (Retina, 15-inch, Early 2013), OS X Yosemite (10.10.1)

But no matter what OS they have they should NOT be using both iCloud Photo Library and USB import as they state they are doing- that will not ever work correctly

When I connect my iPhone by USB and import into Photos, the same image comes in as a HEIC file.

And I believe that if you use ICPL you do not need the compatibility setting although I am not positive - you certainly need it is you are manually importing

And critically once the photos are imported by any means into the Photos library they MUST not ever delete them directly from the Photos library or they will damage their library

LN

You're right Larry. I missed the Yosemite in the profile. If Randy is really still running Yosemite, an upgrade to High Sierra would help a lot.

But do you really think "Which one should I keep in my Photos library in Mac OS?" means, that Randy wants to delete images from the library by modifying the library package? Deleting the duplicated by using Photos to delete the HEIC or JPEGs would be the natural way to do it.

But no matter what OS they have they should NOT be using both iCloud Photo Library and USB import as they state they are doing- that will not ever work correctly

At least we need to be careful not to import older images again. Sometimes we just have to import the photos from the iPhone manually by USB, if we cannot connect the iPhone to the internet for an extended time. But we have to be selective when importing and only import the new photos that have not been uploaded to iCloud and are not optimized.

I’m not using iCloud Photo Library, maybe I should be.

Not necessarily, but it would make things much easier. The only draw back would by, that iCloud Photo Library will upload all photos and videos from your Mac Photos Library to iCloud. You will probably need paid iCloud storage. and if the storage on your iPhone does not suffice to keep your complete Photos Library, you will need to enable "Optimize Storage" on the iPhone and can only work with your photos, if you have a network connection. This can be expensive, if your cellular network is expensive

But how are you automatically importing from the iPhone? You said "Photos automatically imports my iOS photos via iCloud."Are you using My Photo Stream? I that case you need to import all videos and Live Photos using a USB connection, since My Photo Stream does not transfer the videos and the video component of the Live Photo.

If you are taking Live Photos, you must not use My Photo Stream. Then use only iCloud Photo Library or importing by USB.

New photos I take on the iPhone show up in the Photos library on the laptop but not videos. So are you suggesting I turn off Photo Stream and just import by USB (iPhone to Mac)?

At least, if you are taking videos and Live Photos with your iPhone. Otherwise importing by My Photo Stream would suffice.

Or switch to iCloud Photo Library, but then do not import by USB, unless you are away from the network for a long time.