Well it depends on how you define "best". Further you must decide on some hardware first. This is because some hardware only has certain languages supported. You might want to use BASIC but it may be hard to find that an AVR.
If you are a beginner, Arduino is the best way to start IMO. But it uses C. It has lots of pre built libraries and tons of examples.
it seems most hardware supports C/C++ so that is not a bad place to start. BUT if you are new to programming it may be a bit daunting.
In that cause you could use a raspberry PI and then you have m any languages available including Python. You can learn something easy then move up. But controlling servos with the Pi may be a challenge.
If you don't currently know any languages, I would start by learning a high level scripting language such as Python, and find hardware that supports it. If you are up to it, you cant go wrong learning C.
EDIT: There is hardware that also supports C# and VB.NET which are good places to start learning as well. Netduino I believe is still around.
My favorite setup is a Raspberry Pi 2Raspberry Pi 2 coupled with a ChipKit Pi ChipKit Pi for servos, all using C. That gives you a lot of capabilities including SD card storage, multiple languages, cameras, and real time components for using servos and generating signals.
You can also use other languages on the PI as well.
If you want to use Scratch then I'd definitely say use the Raspberry Pi.
(Bad Pun explained: Scratch is the name of a visual programming language that comes packaged on the Pi and could be used to control a robot via scratch GPIO).
There are plenty of examples of using a Pi to control a robot. Python is the most common language used for beginners Pi robotics projects.
