Rarely seeing players hitting the ball off the bounce

I understand there are different heights to hit the ball: off the bounce, at the peak, while it's dropping

Players like Ma Lin seem to vary when they hit the ball. Once he gets an opponent away from the table, it's fun to watch him jump smash one, drop shot another, and then hit off the bounce down the line. The same goes for Oh Seung Eun. Even during regular rallies, they would vary their timing.

However, most pros now seem to hit while it's dropping or at the peak to powerloop.

I've had some older club players tell me to hit the ball earlier which confuses me. 

Is it a generation thing or just a preference? And what should I be focusing on?

Taking the ball on the rise is normally done when blocking, but sometimes when looping as well. At the world-class level, most try to loop at the top of the bounce, but some do it off the bounce. On the backhand side, where the body is in the way, backhand topspinning off the bounce is often the norm. 

For most players, I recommend top of the bounce or just afterwards. Some styles will back up more, and that's okay if you only do so when forced to. (Xu Xin often backs up a lot, and he's top five, former #1.) 

Few world-class players rely these days on the dead blocks that Ma Lin used to do, though many players still do this occasionally. They are instead trained to attack relentlessly, and it seems to work.