Trad vs Roth 401k Contributions

So I just found out my work has a Roth 401k option. Up to now I’ve obviously only been doing traditional 401k contributions. But moving forward is it more worthwhile to do Roth contributions? Or some combination of the two.

I’m 40 years old, I’ve got about $250k in there now, my job does a flat 3% contribution regardless of my contribution, and I’m about to start maxing my contribution (which I know should have been but can’t go back now). Everything goes into a low fee S&P 500 tracking fund.