Don't just consider the brand. You have to consider the line/model.
Lenovo's consumer lines (Ideapad, Legion, and others) are all absolute garbage, and you shouldn't consider them for even a second. But their enterprise line (Thinkpad) is generally very, very good. The main problem is that they're expensive.
Asus is strictly consumer-grade. They do not have an enterprise line. Their build quality is among the best you can find in consumer-grade, but enterprise-grade is always higher quality than consumer-grade.
I would never leave an OEM load on it, so privacy isn't much of a concern for me. I suspect they're both pretty bad in this regard.