Playing The Meta

I'm going bring up a somewhat controversial topic but I genuinely curious to see what you guys think. Is it better to stick with the champions you know and play them in Solo Q or should you play champions that are in the spotlight. Obviously there are exceptions to everything but when it gets down to it what is better as far as success goes. For example, late season 3 the best Kassadin player in the world would have an insanely high win rate probably upwards of 80 percent if he could manage to get Kassadin every game back when he was insanely strong, now however, the best Kassadin player in the world all though should be able to find success would be much worse off solely because Kassadin is so much weaker. From a middle lane perspective, is there a specific point where you drop Kassadin and start playing the ever so popular champions (Ahri, Katarina ect.) because they are more powerful and can more easily carry? The meta changes pretty frequently as much as every patch or so. Is it worth it to refresh champ pools frequently with powerful picks or to hold out and play what you know regardless of stats.