Quicken is great software itself, but suffers the most in the area where it should not: importing user's data (bank statements, credit card statements, investment activity).
You basically have the following situation:
your bank lets you download your data in different file formats
your Quicken software allows you to import data in several formats with some conditions
you are lucky if both sets above cross each at least at one point (you can download format that Quicken will accept)
are not lucky if your bank does support Quicken format, or Quicken does not like your bank (for some unknown reasons)
There is also another situation when you have data in some format (for example, Excel spreadsheet), and you are switching to Quicken, but would like data to be migrated to Quicken as well.
The following tools should help to get your transactions inside Quicken in the most easier way:
CSV2QIF - if you have transactions in CSV, Excel or other spreadsheet file format, you can easily convert your data to the QIF format. CSV2QIF creates files compatible with Quicken earlier than, Quicken 2005, Quicken 2006, Quicken 2007, Quicken 2008, Quicken 2009, Quicken 2010, Quicken 2011, Quicken 2012. QIF format is not fixed format - it can have slightly different variations, and Quicken will not accept all of them. Having said all that, CSV2QIF creates Quicken compatible QIF files. There is one catch with this conversion - you have to tell CSV2QIF exact account name you have in Quicken under which you want to import data (in other words - when you are importing QIF file under Quicken, you have to select "All Account", not a particular account).
CSV2QFX - this tool is very similar to CSV2QIF, but creates QFX files instead of QIF files. With CSV2QIF you have to specify account name, but with CSV2QFX you don't have to. So should we then just create QFX and leave QIF alone? There is another catch - for QFX files, Quicken goes online (you have to be online to the Internet during import), and checks if it likes the bank specified in your QFX file (for QIF import no online check is done). So your QFX file should be 'likable' by Quicken. CSV2QFX resolves this issue. Supported all Quicken versions, including Quicken Essentials for Mac.
Bank2QIF - this tool can convert whatever bank file you have (OFX, QFX, OFX, QBO, QIF), and convert to a QIF file acceptable by Quicken. Again, as for CSV2QIF, you have to specify account name. Sometimes your bank supplies the transaction files with the account name, so Bank2QIF provides the mapping dialog for renaming the bank account name to match what you have in Quicken).
OFX2QFX - this tool converts OFX file to QFX format. OFX and QFX formats are very similar, with QFX format is being an 'extension' of the OFX format. OFX2QFX 'enriches' OFX to make acceptable by Quicken. As for QFX format, all details described above for CSV2QFX apply here as well.
QIF2QFX - this tool converts variations on QIF format into QFX format. Quicken versions up to 2015, 2016, 2017 for PC or Mac are supported.