This short writing lets you know the New Import Flat File Wizard in SSMS 17.3.
Import Flat File is one of the most common features to use for any kind of developer. The new import flat file wizard will get you default text type is nvarchar than varchar. That is the most likely part for me.
If you are lazy to watch this video, https://channel9.msdn.com/Shows/Data-Exposed/Introducing-the-new-Import-Flat-File-Wizard-in-SSMS-173?term=ssms%20flat%20file. Then you can see the Import Flat File from the following screen on top of Import Data. I have tried it and it is working well for now. But Ctrl-Z does not work in Modify Columns page.