Python/Ruby - 2 high level languages which has great learning curve, meaning that you will learn them quick, and can produce great results in no time, can run on both linux&windows machine
C - great for quick stuff - automations that should be really quick - I dont think that such type of automations are the thing you are looking after. also the learning curve is worse, you will have to put lots of time before getting something working, will run on both windows & linux but will need to "port" (alter the code) to support the operation system
Java/C# - has a good GUI support. it is useful to intergrate with an existing applications (especially microsoft's) - learning curve is in the middle, will run on windows and linux (C# will need some porting to run properly under linux environment)
imacros scripting language - really quick learning curve, great results. the main con is that it should run on windows machine, which costs more money than linux machine.
good luck!