I raised a lot of competitive pokemon on the advance generation games (the real games, not netbattle), but unfortunately I have not gotten to ever really use them because there is no one to play pokemon with when you are my age. So while I may have the pokemon, I am not that skilled with using them yet since I really have not had that much practice.
Its actually LESS time consuming to raise a competitive pokemon because you get all your stats way before even LV 50, once you know what you are doing there is less tedious leveling up, and training for EV's really doesn't take long at all if you have the macho brace and pokerus, thankfully I have that.
With D/P you don't even have to have your pokemon at LV 100 since you can set the battling level at either 50 or 100, you just have to get your EV's and the moves you want. So you can have a lv 30 pokemon with all its EVs and the moves you want and be ready to battle at level 100 if you just set the level at 100, it will automatically be raised to LV 100 for the duration of the battle. The only reason you have to level now is to get a certain move if you want that move, or to beat the game. I am convinced that Nintendo has really done it with these game, they have REALLY made a difference with these pokemon games, making it less tedious and more fun!
So its a mix for me, some competitive and some casual, I do like the challenge of raising that perfect pokemon, it certainly extends the game play of these games to infinite proportions.