It depends in part on how often the field is needed by the user. If the field is usually empty or has minimal information (maybe 2 or 3 lines), then a "view more" approach is appropriate. But if the field often has 8+ lines of text, a scrollbar will be better. You can also have a special condition to limit the maximum size of the textbox, so the "view more" link can create a scrollbar if the text is 20+ lines, because you probably do not want that text to fill the entire screen if someone types their life story into it.
For editing, I suggest that the box has a scrollbar. If you want to make it more advanced, the box can expand dynamically as needed, and a scrollbar is added when the text approaches a set size limit. As an aside, I suggest that you set a large inner-right margin on the text, so that the sudden addition of the scrollbar does not reformat the text.
The goal is to reduce any wasted space on the page, so there is no reason to have a large field for a small amount of text. And if there is a large amount of text, you probably don't want it to dominate the page.