They are both acceptable, so is “stream of thought,” but train appears to be the most popular, and that is what they are all listed under in Wikipedia:

http://en.wikipedia.org/wiki/Train_of_thought

I personally prefer train as well.

Chain Of Thought

Train

This Site Might Help You.

RE:
Its it My Train of Thoughts or My Chain of Thoughts?
When someone says the have lost their _____ of thoughts? Which is it?

I have a beagle that is an escape artist. We have tried all types of collars and harnesses but she manages to get out of them if she sees something she wants to chase. We use a choke chain on her only when she is in the yard on her chain, or if we know we are going to be walking where there is wildlife (like rabbits) that she might want to chase. She is an indoor dog so when she comes in the chain comes off. And if you crate your dog NEVER have a collar of any type on them. When we are out with her on her leash and she is under our control we use a regular collar and it is fine. So I think choke chains are fine if used properly. Just make sure that if you use one on a dog that stays outside to check it frequently. I used to work at the Humane Society and had dogs come in that were left outside and had the chain get to small for the dog and grow right into the neck.

I always thought it was train of thought, not thoughts.

Neither. It is train of thought.

I’ve always said “Train of thoughts” but come to think of it, “Chain of thoughts” does sound more credible.

However, I still think it’s “Train”.

It’s train. Chain doesn’t go well with the sentence.

TRAIN

choo choo