(The links in this post may be affiliate links. All this means that if you click on a link and make a purchase, I will receive a commission. This in no way increases the cost to you, and may even help you save money. Thank you.)
Ideally, my answer is that if you CAN do both, that's the safest way. I personally use both. However, even if you use both, one has to be the priority method for organizing, tagging and sorting. Ultimately, you have to pick the option that you are more comfortable working with and that you will regularly USE.
For me, after several years of deliberating this question, my answer was really made for me by the way my family takes photos.
Depending on how long you've known me, that may surprise you. I've been teaching how to use Historian since 2007 when it was Memory Manager. And I've been a huge advocate of the things this software can do to organize and safeguard your photos. I still use it for some of the same reasons I started using it 13 years ago.
But, if I'm realistic, I realize that most of the photos my family takes are shot on a phone. And not just one phone. My photos now are taken by me, my husband, my daughters, and my mom, for the most part. And it's much easier to have my husband's phone automatically upload his photos to my Forever account and then work with them from there. I also have my photos set to automatically upload. My daughter uploads hers to her account, but we share easily between our accounts. And when I share with my mom, I put the photos quickly in a shared album in my Forever account so she can add them to her account or download them.
Plus, since I work with multiple computers and devices throughout the day, it makes sense to organize on the platform I have the easiest access to. That is my Forever Storage account. I can only have Historian and my main memory vault loaded on one computer. And if you've read any of my posts over the years, you've seen how many times operating systems or hard drives have failed on me and I suddenly have to reload everything on a new computer. As I get older, I am less and less patient with that process. Don't get me wrong: As long as I'm running my shadow copy in Historian regularly, it is not that difficult to restore and I don't lose photos or organization. That's one of the best features of Historian. But, I love the peace of mind that my laptop can die tomorrow and I can get to my organized photos easily on my phone or tablet while I'm waiting to get a new computer set up.
The cool thing now is that no matter which place I start, the tags I create can carry over to the other method so I don't have to do everything twice. I start in my Forever Storage account and work through deleting unwanted photos, tagging them and possibly arranging them into albums in my account. Then when I download my tagged photos after I've done the work in my storage account, the metadata from the tags I've already added is saved in the photo file and those tags are then imported with the photo into Historian. I personally now use Historian more as my local backup of my photos so that I can retrieve them when I'm offline. But, if you're more comfortable starting the process in Historian, it would also work. After tagging and selecting photos in Historian, when you share to Forever Storage the photos will have that metadata embedded in them and the tags will stick with the photos in your Forever account.
Whichever way you choose to do it, make sure you DO do it. That's the most important part.
Let me know if I can help.