Oliver McCall. Why? Because I can't see Shannon outpointing him and definitely not scoring a knockout. Reversely, Oliver could do both.
This is a battle of toughness right here, and I see Briggs getting beaten badly in that, McCall was too tough... it doesn´t help that McCall was also more skilled than Shannon....
If Briggs goes toe to toe he would be hurt and kod. I think Briggs would box cautiously and eake out a close decision. McCall has the better wins and I rate him higher, but styles make fights and if Briggs used his height and reach and boxed cautiously, he wins. McCall wasn't too effective when the opponent boxed and he wasn't too busy. See the Holmes fight where a faded (badly) Holmes almost pulled out the win. Briggs W SD 12 McCall
Briggs just never had a high punch output. His work rate is one of the worse I've seen. If dude was busier he'd have a bit more success. I see Briggs going for the knockout, punches himself out and McCall drops him for good around 8 or 9 rounds.