Which is better - cakes or bulk substrates?

If you are a beginner and want to grow just a few mushrooms, then cakes are better for you since the whole process is shorter and bears less chances of failure.

Growing cakes is a testing grounds for your skills. If you can't get PF cakes to colonize clean, then you will almost certainly fail with grains,  or bulk substrates.

Once you have managed to grow cakes and have a feel for it, you can advance to better yielding methods.