All your options are grammatically correct, however I believe (without knowing the context it’s hard to be sure) that while 意见 is often translated as “opinion,” the word “suggestion” might work better for you. My Chinese is fairly basic, so I’ll give you the definition of both words for you to sort out: English definitions: Opinion — one’s mental attitude or view. Suggestion — an idea or plan that one puts forward for others to consider. If I’ve understood your meaning (difficult with my poor Chinese and without context), a good translation might be “I think he has a good suggestion” or “I like his suggestion / idea / plan / proposal (the best).”

i prefer 3

I prefer, "I think he has a good opinion" but "I think his opinion is good" is almost equally good to my ears.

The first two both work. I would personally use number two.