Is it better to DCA or buy one lump sum of ETFs to reduce commission paid?

For S&P, Lump sum. Yes the commission and sales charge will eat up your profits.

But at the same time, save more money and do DCA with lump sum. Means each time you DCA, you do 10k. DCA need not be a monthly thing. It can be every 6 months or 1 year.

Personally, I feel that DCA will underperform lump sum investing in the long run because you are buying into the market at varying market conditions during every period, while lump sum if done at a suitable timing, will generate higher returns.

However, if you are more risk adverse, then DCA will definitely feel safer an investment. Though I would disagree that there is much risk in your context, because to me, the S&P index is a relatively safe investment (with historical returns of 10%) and you will definitely have positive returns in the long run (10-20 years horizon).