There's no single answer to this question, so let's look at a few scenarios:
If you want to fly overseas, Qantas Points offer access to reward flights with 29 partner airlines, including oneworld alliance members. Velocity Points offer access to reward flights with 9 partner airlines.
If you want to fly in Australia or New Zealand, both Qantas and Velocity Points give you plenty of options for economy, premium economy and business class reward flights.
If you want reward flights only a few months before a trip, we found better availability with Velocity when researching this article. Specifically, in August 2023 we looked at a 7-day return trip from Sydney to Queenstown in November. Velocity had both economy and business class reward seats available for return bookings, while Qantas only had return economy reward seats and a one-way business class reward seat. Both offered points plus pay, but that is typically less value per point.
If you already fly with one airline more than the other (e.g. Virgin Australia), focusing on earning points with the linked frequent flyer program can help you redeem reward flights faster.
You can weigh up more details in Finder's guide to Qantas vs. Velocity Frequent Flyer.