As a lone striker, regardless of who we are playing, I would rather see Rondon.
Berahino is a superb finisher...but the rest of his game is seriously lacking. Rondon would have more joy in the role of a lone striker.
Playing both gives us options. Rondon to me is the old fashioned centre forward, does really well facing the goal & can score with his head, but relies on service from wide play.
Last season, Berahino was anything but a superb finisher, he missed chance after chance he should have put away. He realised he had been stupid, & his confidence was totally shot. Somewhere in there though is a very good footballer, he has the skils, & the vision & the composure to do a very good job as a number 10, hopefully he'll do that for us between now & Christmas, what happens after that, who knows?