It depends on your goals, and I often use RootsMagic for this purpose, meaning that I export my Gramps tree to GEDCOM, import that into a new RootsMagic database, and compare that with FamilySearch.
My main use then is either to correct some data that is already there, by selecting persons and adding or replacing things one by one, or to download new branches, and make notes of the persons where these branches start.
In the latter case, I export the full RootsMagic tree into a new tree in Gramps, so that I can run some quality checks, and then I export the new branches which are either ancestors or descendants of existing persons, in .gramps format.
When I import such .gramps files into my main database, I know that in most cases, there is only one person to merge, which is the former end-of-line person. This may be an end-of-line family, so then I have two persons to merge.
Note that, although Gramps forces you to pick one person in its UI, it does not throw away anything of the other person. The new person can only have one ID, but the ID of the other person will be added to the person’s attributes. Names will be added as alternative names, and all events will be added as extra births, marriages, deaths, etc., even if they are exactly the same for both persons before you started the merge.
I mention RootsMagic here, but you can also do this with Ancestral Quest and other programs. I mention these, because I like both, and these features are available in the free versions of either.