New basement - want to seal concrete

Best product depends on your criteria for best.

Personally I use a flat (non glossy) concrete floor paint, water based so cleanup is easy. I'm not fond of gray concrete as a finished look, so unless the concrete was dyed some other color I don't want to see it - your mileage may vary, they do make clear concrete sealers if you like that look. Paint cuts dust generation, and improves lighting if you use a light color.

Some folks like to spend a lot more on epoxy coatings and then spend some more on making them not slippery.