You can use any of the three methods to find the index of the first occurrence of the value 3 in the array. However, the np.where() function is the simplest and most efficient option. The following code shows how to use the np.where() function to find the index of the first occurrence of the value 3 in the array arr:

```python
import numpy as np

arr = np.array([1, 2, 3, 4, 5])

# Find the index of the first occurrence of the value 3
index = np.where(arr == 3)[0][0]

print(index)
```

This code outputs the following:

```
2
```

The output shows that the index of the first occurrence of the value 3 in the array arr is 2.
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