Arduino is a good microcontroller for DIY and hobby projects. But when you are thinking of making something that has many actuators and sensors and requires very fast processing, then you would need to think of other alternatives. Also, Arduino is not multithreaded (not really a requirement for me).
So, what better microcontrollers that are not very expensive (1000$+) and is used in robotics?
I prefer something that is well supported and has a text-based programming language (Not LabView for myRIO for example).