Comparing the Lego servos in the EV3 kit to the Dynamixel Servos in the Bioloid Stem Kit.

Servos are always the key to your robot and how well it will perform. A good servo can turn a bad robot design into a robot that will work, just as a bad servo will turn a good robot design in to an unusable robot. 

So I think this comparison is important in understanding the strengths and weakness of each kit and which kit would be the best one to buy.

In the Bioloid STEM Kit there are one AX-12A and one AX-12W Dynamixel Servos.

Robotis Website.

In the EV3 kit there are two Large motors and one Medium motor.

Lego website.

It looks like the best comparison is the Large Servo to the AX-12A and the Medium Servo to the AX-12W.

If you look at the stats below the AX-12s pretty much dominant the Lego servos in almost every category. Yes you get one more servo in the Lego kit then in the Bioloid kit but for me the decision is simple! I am going with the kit with the better servos. 

The EV3 Large Servo Motor is a powerful motor that uses tacho feedback for precise control to within one degree of accuracy. By using the built-in rotation sensor, the intelligent motor can be made to align with other motors on the robot so that it can drive in a straight line at the same speed. It can also be used to give an accurate reading for experiments. The motor case design also makes it easy to assemble gear trains.

• Tacho feedback to one degree of accuracy 
• 160-170 RPM
• Running torque of 20 N/cm (approximately 30 oz/in)
• Stall torque of 40 N/cm (approximately 60 oz/in)
• Auto-ID is built into the EV3 software

The EV3 Medium Servo Motor is great for lower-load, higher speed applications and when faster response times and a smaller profile are needed in the robot’s design. The motor uses tacho feedback for precise control within one degree of accuracy and has a built-in rotation sensor.
• Tacho feedback to one degree of accuracy 
• 240-250 RPM
• Running torque of 8 N/cm (approximately 11 oz/in)
• Stall torque of 12 N/cm (approximately 17 oz/in)
• Auto-ID is built into the EV3 software

Best place in the US to buy Robotis products is at Trossen Robotics.

Lego EV3 website.