Start with whatever you want, write raw SQL or use an ORM, your choice.
If you find yourself doing a bunch of string formatting and concatenation, then use more ORM features. The more loops, if-statements, and regexes[0] involved in your "raw SQL", the more important it is that you start using a proper ORM.
If you find yourself struggling to get the ORM to do exactly what you want, and you're repeatedly reviewing the SQL it generates, then use less ORM and more hand written SQL. Check to see if your ORM allows writing only a portion of the SQL by hand (SQLAlchemy does).
Start with whatever you want, write raw SQL or use an ORM, your choice.
If you find yourself doing a bunch of string formatting and concatenation, then use more ORM features. The more loops, if-statements, and regexes[0] involved in your "raw SQL", the more important it is that you start using a proper ORM.
If you find yourself struggling to get the ORM to do exactly what you want, and you're repeatedly reviewing the SQL it generates, then use less ORM and more hand written SQL. Check to see if your ORM allows writing only a portion of the SQL by hand (SQLAlchemy does).