Last month, I started this poll, which asked "Which IoC Container will you use for your next project?" in "C# Developers / Architects" LinkedIn group (I thought the group has 115K+ members so would get more responses) and got 19 responses and 3 comments only :(
I put it all into this chart:

I got two comments in favor of Ninject so treated as separate option.
The Top 3 preferred IoC Containers are Unity, Autofac and Castle Windsor.
Here are useful resources if you want to do comparison study of different IoC containers:
IoC Container Benchmark - Performance comparison
How do the major C# DI/IoC frameworks compare?
Next Poll:
What is your preferred Javascript MV* Framework for your next project?
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Enjoy IT life !!
Note: If you missed the poll, don't worry, you can share your thoughts in the comment box.