Which feed type should I choose, API feeds or file (XML, CSV, TSV ) feeds?
API feeds update individual products data change (prices, stock, description, title) instantly (in paid plans). However, since they are rate limited by Google API, they can be slow for cases that require mass product updates, including the initial run, regular re-new runs and foreign currency rate update runs (for foreign currency feeds).
API feeds do not remove products. Products no longer in feeds are just stop synchronized and left in GMC for expiry. If items need to be removed from GMC quicker, remove them in GMC manually, or switch to file feeds.
File feeds (XML, CSV, TSV) do not update individual products, but every time they run, they update the whole portfolio part that is included in feeds. File feeds are not subjected to Google API rate limits so they are much faster than API feeds for mass updates, that is why they are recommended for foreign currency feeds. In fact, file feeds can be suitable for most of the use cases, even for fast stock changing portfolio (Google bot can help to sync individual stock updates by crawling the landing page). File feeds are run:
1/ At least once every 24 hours.
2/ If it is a foreign currency feed, when the corresponding Shopify currency rate update
3/ When a new feed settings is saved