Brushless motors - in a nutshell - eliminate the internal brushes and wear of older brushed motors, which cause a lot of internal friction and wear out much sooner.  Most - but not all reliable brands have switched to using Brushless High-efficiency motors in their power equipment.
In addition, Brushless motor tools last an estimated 2-3 times longer than tools with brushes.
The best type of motor to invest in, if your budget allows is a power tool manufactured with a “Brushless Motor.”