Sometimes, other times

How would you say this please?

Sometimes he is nice, other times he's not.
Sometimes he is nice, at other times he's not.
Sometimes he is nicer than at other times.
Sometimes he is nicer than other times.
Sometimes he is nice, others he's not.

Sometimes the questions are harder than other times. Sometimes the questions are harder, other times easier.
Sometimes its more difficult than [at] other times. Sometimes it is more difficult, other times it is less difficult.
I'm more tired some times than [at] other times. It depends on the day.

Sometimes it takes longer than other times.
Sonetimes it takes 5 minutes, [at] other times it takes longer.

Sometimes the drinks taste better than other times.
Sometimes the drinks taste better than other drinks.

Thank you