I'd say that (clause)
You use the phrase "I'd say that..." to share your opinion. It's similar to "I think..." but it sounds more thoughful. It demonstrates that you're still not completely sure of your opinion.
Here are some examples:
A: What do you think?
B: I'd say that the first one would probably be better.
I'd say that drinking four or five nights a week is probably a little too much.