Good question. The answer to this is "It depends" upon many factors like are you looking for a tool for which you don't incur any additional cost, Is your company already using third party connectors which you can leverage, do you have people who can work on Java or .net if you take that approach, what kind of licenses is your company upon.
Here are the multiple ways that Integration can take place with Anaplan
1. Anaplan Connect - Free to use but you need to write batch or shell scripts, You also need third party scheduler Like MS Task scheduler with it
2. Third Party Connectors - Mulesoft, Snaplogic, Dell Boomi, Hyperconnect, Informatica Connector. You have multiple inbuilt connectors with these options. Hyperconnect (my favorite) as it has hundreds of inbuilt connectors. (Note: Two connections in Hyperconnect is free of cost with enterprise edition license)
3 Rest APIs: This is the most complicated one but it is highly customizable. Works with Java and .Net also
4. CloudWorks: Cloud to Cloud Integration - As of now it can only be AWS S3 as source and target but I believe they are working on it to open it for other cloud platforms as well.
Honestly speaking I have used Hyperconnect with SAP and Oracle ERPs. I haven't noticed if we have something for IQVIA or Integrichain. Let me loop in true integration champ here @ben_speight . Sorry Ben if you are not the right person to help the gentleman, I couldn't think of any other person than you.
I can't comment on this specific use case but if you start with tools with which you're already comfortable then that reduces the initial cognitive load. Using files splits the problem up into separate pieces (extract, transform, upload, import) which can be helpful in the early stages but you'll need to store them somewhere, which can be a concern unless either your filesystem encrypts data at rest, or you are testing with dummy data. Once you have a handful of basic integrations running, explore other ways of achieving the same ends and see if they work better for you.