As per the wiki's page on Balor's Magical Eye, the highest known-for-certain power level recorded in Nanatsu no Taizai is Ludociel's impressive 201 000 (Chapter 286, page 14). However, we know that Mael has a 200 000+ power level (Chapter 278, page 12). As this is relatively vague, Mael may or may not have a numerically higher power level than Ludociel.
Since Mael has often been described as the strongest Archangel in-universe, it is almost certain that his actual power level goes beyond 201 000. Alas, since it has never been recorded precisely, we cannot actually confirm this.