Could you give me a suggestion for the "best" or a good negative scanner that can take negatives at least to the size of 6x9 ?
A "good" scanner would be the Epson V500. Maybe not best, but good, and a good value. I bought mine new and have used it for several years. I am still learning how to scan well, because there are so many things you can change to alter the result. I scan 35, and three sizes of medium format; 6x4.5, 6x6, and 6x9. I even scanned some negatives from World War I, they were 100 years old, and filthy dirty from being in an attic. The film was slightly wider than 120, so the scan missed the edges, but the results were far, far better than I expected from the dirty negatives.
The medium format window is a little small. I have to cut the film to one each of the 6x9, so that's a problem. Also, I don't have a way to hold the film flat, and curly film doesn't lie flat in the holder.
I would like to have a V750, which takes bigger film (for large format) and has bigger holders that hold more film for one scan session, and I would like to have a way to hold the film flat. But on a budget the V500 works ok. The software is good, but takes some getting used to. The screens that pop up don't always make it real clear how to change things, some things seem hidden away, and you have to use different windows to change things that should all be on the same window.
I haven't used other scanners, but I hope my experience with the V500 can help with your decision.
Jeff