best way to iterate through elements of pandas Series

All of the following seem to be working for iterating through the elements of a pandas Series. I'm sure there's more ways of doing it. What are the differences and which is the best way?

import pandas


arr = pandas.Series([1, 1, 1, 2, 2, 2, 3, 3])

# 1
for el in arr:
    print(el)

# 2
for _, el in arr.iteritems():
    print(el)

# 3
for el in arr.array:
    print(el)

# 4
for el in arr.values:
    print(el)

# 5
for i in range(len(arr)):
    print(arr.iloc[i])

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