For cdrama it depends on the production and actors. Usually if the actors are good their projects are great too - a few examples:
Barbie Hsu - Meteor garden, mars, summer's desire
Ariel Lin - Prince of Lan Ling, In time with you, ISWAK (really not her fault that the character is dumb. If you compare it to the other versions I think she did briliant work with what she had. Also the only version I could some what stomach), Love Contract
Zhao Zanilia - Princess Agents, The Mystic Nine, The Journey of Flower, Boss&Me, The Palace
Liu Cecilia - Scarlet Heart, Sound of the desert, Imperial Doctress
Huo Wallace - I'm pretty sure you could watch any drama he acted in and love it because he's just that great and u ignore anything else. Of course his more recent dramas are more well known like Love me if you dare, Imperial doctress, Battle of Changsha, The Journey of Flower, The perfect couple. Love at first fight was ok as I remember (watched a few episodes many years ago, maybe even before this site existed)
Ones in a while there is a drama that just has a great cast of actors that later branch out to more greatness - like in Ten Miles of Peach Blossoms (lots of greatness!) , Chronicle of Life, Lady and Liar, Princess Agents (I'm pretty sure even the side actors would be great in a few years), The Princess Wei Young also good. Other good actors are Hu Ge, Tiffany Tang, Feng William, Zhang Vin (on the rising now), Dilmurat Dilraba.
Another thing is I feel that for modern drama taiwanese is better, while for historical ones chainese is usually better. Overwhole for me cdrama is historical ones cuz they are just made better with more money and effort put into.
As for jdrama I believe there is a trend that went away in it. A few years back they were good and it's like after the era of Hana Yori Dango it just went downhil. You should try the old ones - sure the filming quality isn't great but the acting and even the scripts are so much better in my opinion. Nowadays I almost can't stand the new jdramas coming out even if they are with actors that I liked previously, and I just regress to the ones made around the 1995~2007. I can really rant a lot about this subject.