Boldin. Fitz relies more on being an athletic freak. Boldin is great of perfect route running, awareness, and smarts. So a big injury is way less likely to effect Boldin than Fitz. I'll take Mr. Boldin.
I would personally go with Fitz. Like everyone said it is his 3rd year and could be his magical year. Fitz also is a great route runner and has good hands. I think they will be looking his way a lot this year.