What's the difference in meaning between "I never would have thought..." and "I never have thought..."?

Solution 1:

I never would have thought

this indicates that not only has the thought never occurred to you, there is nothing you can think of that would have caused the thought to occur. It is an expression of surprise at whatever the subject is. e.g. I never would have thought that Bob was capable of robbing a bank!

I never have thought

this means simply that you have never had this thought before, but not indicating any surprise. e.g. I never have thought that Bob was very nice.

Solution 2:

I never would have thought.

States that you would have never, if given the chance, have thought that something would happen.

I never have thought.

States that you had not, until now, thought that something would happen.