Exporting directly to your final delivery eg. Mp4 should result in higher quality output since there isn't any loss when converting to an intermediate format. But prores is designed as a high quality intermediate codec so you're unlikely to spot much of a difference.
I'll go with prores hq (and I usually use that as an intermediate to/from grading), but for your purpose, you're unlikely to spot any difference as the Mp4/h.264 compression you will use is so much lossier.
So usually I'll go with efficiency in process. Eg. If my final master is to export a prores master, I'll export the master and encode h.264 screener from that file. Which is faster than having to render the raw files twice.
Just make sure you're not already rendering to I frame mpeg in the timeline and "using previews" for export!
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