- "Did you enjoy the film?" "I'll Say."
I'll say! used to show that you agree very strongly with what has been said.
- "Does he eat a lot?" "I'll say!"
'I would say' and 'I guess' have the same meaning?
- I would say he is not coming.
- I guess he is not coming.
A participant says:
They have only very approximately the same meaning, in that both imply some degree of uncertainty and leave room for others or for facts-on-the-ground to contradict what follows.
- I would say characterizes what follows as a personal opinion or judgment: ex) From what I know of him I would say he is coming.
- I guess characterizes what follows as a conjecture or inference: ex) Well, if he were coming he'd be here by now, so I guess he's not coming.
But there's obviously room for some overlap: an opinion may be based on inference, and a conjecture may be based on opinion.