Do you think is it good to elect someone as President for life or is it better to hold a regular election after every few years?

No, I think it is better to have a regular election.

By giving power to one person without any time limit, reduces their accountability and chances of good governance also reduces.

Regular election keeps checks upon the leader and the parties and gives a chance to other parties and contestants to get elected and form a government.

Example: In Zimbabwe, Mugabe was president for a lifetime, this led to corruption in the governance and reduced the efficiency of the ruling.