This is my 2c.
Things are ever changing in the point space, as we have noticed especially in the last 1-2 years.
I always encourage collecting flexible points instead of deciding on one particular program or points to stick to. As if you decide to collect just points A from Program A; and for what ever reason the program devalues (requiring more points for redemption, reduction of available award space, etc), you are stuck with a bunch of points that you struggle to use.
Flexible program include Amex membership reward program. With flexible points, you stock pile the pts. When you need to use them on flights, you check whether there is award space with different airlines before transferring pts to that program that allows you to redeem that seat on that flight.
Qantas and Velocity are the easiest to earn in Australia. This is a double edge sword. More people have Qantas and Velocity points in the disposal->lots of competition when looking for award seats.
For travel to EU, Qantas mostly has options like, Emirates, Cathay Pacific, Qatar. However, award space has become a bit eratic for what used to be quite reliable (Emirates and Cathay Pacific).
With Velocity, the 2 main options are Etihad and Singapore Air. I would personally stick with Singapore Air to avoid the large Etihad surcharge. The increase in transfer rate between Velocity and Krisflyer is also problematic if you want to transfer to Krisflyer. Not so much a problem if you use Velocity pts to redeem Singapore Air seats directly.
If you were asking of which programs to start building your status with, it really depends on what airlines you generally fly with. You can credit flights to partner airline programs or alliance member programs. E.g. crediting Thai Airways flights to Krisflyer.
Hope that answers more questions than raising more questions.