How to handle data migration and data transformation tasks when moving data into Salesforce CRM?
I would recommend XL-Connector or XL-Connector 365 for the export/import operations.
Being able to upload directly from VLOOKUP formulas and having a two-click way of switching between orgs will save you a ton of time. Additionally, you can write Ids from the bulk Insert operation into any column of the existing data having a super quick way of loading related records. The operation results are written right next to the data, so if something's wrong – it takes no time to spot the problem, correct it, and reupload.
Disclaimer: I work for Xappex, the maker of these tools.

