I always only recommend using a metal madeleine pan to get the best results. Silicone doesn't convey heat the way metal does so madeleines tend to not rise as much in a silicone pan. I use this Aluminised Steel Madeleine pan. That being said, when you make madeleines with a chocolate shell like here, it is the only instance where you could use a silicone mold as it will be easier to pop the madeleines out once the shell has set.