These systems can both be used for different purposes. So don't ignore one system over the other. The main difference is that VFX Graph uses GPU for particle simulation and uses Shuriken CPU.
VFX Graph uses GPU particle simulation and can simulate more particles with lower resource costs. It's perfect for more complex simulations, but also for simple ones! Note that GPU particle simulation requires devices that support compute shaders, so not all smartphones support this yet. The VFX diagram is perfect for effects that are largely visual and do not require interactivity with the physics system (think environmental influences like smoke, fire, water simulations, etc.).
Since Shuriken uses the CPU particle simulation, it has access to the main physics system so you can give the particles more interesting properties and get information about them as they are viewed as floating objects. For example, when a particle hits an object, it bounces back at a faster rate (you can do this in VFX Graph too, but with a limited number of particles). You can also access each individual particle through code and find out its position, color, and other particle characteristics. Shuriken is perfect for gameplay effects like battle spells and flying debris (something that would require information from the physics system).
I would recommend starting with Shuriken and, once you're ready, learning VFX Graph. Both systems are functional and both systems are used in creating effects. This only depends on the application.