Ben Roethlisberger ranks No. 10 among quarterbacks in both Jamey Eisenberg's and Dave Richard's lists. This is pretty much a consensus ranking for Roethliberger - ESPN and Yahoo! also have him at around the same place. The key with drafting Roethlisberger isn't necessarily his exact ranking among quarterbacks, but how you value quarterbacks relative to running backs and wideouts. We at SB Nation Pittsburgh advise avoiding quarterbacks in the first few rounds and grabbing backs and receivers instead, then taking someone like Roethlisberger in the middle rounds.
Rashard Mendenhall ranks No. 12 and No. 14 among running backs, which pretty severely underrates him, in my opinion. Mendenhall should get a ton of carries in a run-happy offense, and should therefore be a top fantasy performer. If he's available at the end of the first round of your draft, you should take him.
Mike Wallace ranks No. 6 in both lists among wideouts. This is, again, pretty much where he's ranked at most fantasy services. Hines Ward ranks No. 39 and No. 34, which might actually overrate him slightly - he's at the tail end of his career, and might not see as many opportunities as usual thanks to the emergence of Antonio Brown and Emmanuel Sanders. I'm not sure I'd go so far as to say you should take Brown before taking Ward, but if I were drafting, I'd let someone else overrate Ward.