Arduino Uno Rev 3 is an excellent board. This is the most popular Arduino board, and one of my favorites. The ATmega328P microcontroller on the Uno has been used on Arduino boards the longest of any microcontroller. This means that it has the best level of official and community support.
The Uno doesn't have an IMU, but you can buy IMU modules or shields and attach them to the Uno.
One thing to note is that the Uno uses an 8 bit microcontroller that doesn't have as much memory or processing power as the newer Arduino boards. For many projects, the Uno is plenty capable. People have done very advanced, complex project with this board. The really nice thing about the ATmega328P is that it's relatively easy to understand how it works. If you ever decide to learn the low level workings of a microcontroller, you'll have a much easier time with the ATmega328P than you would with the ATSAMD21G18 microcontroller used on the Nano 33 IoT or the dual core x86/ARC of the Arduino 101's Intel Curie module. However, if you need to do very memory or processing intensive operations, as may sometimes be needed for advanced processing of IMU data, you might get frustrated by the limitations of the Uno.