My vote is for the Challenger. If the Simplex is a usual plastic one, I think that the metal Huret will shift better and not twist as much under shifting pressure as the plastic Simplex. This is just my opinion. I really never liked anything Simplex made because I think that they never shifted will, either front or rear. I recently sold an older Raleigh Super Course with Challenger front and rear derailleurs and felt that the bike shifted very well. Good luck in your choice.