Infernape and Empoleon get a fair amount of usage in competitive. Infernape is your standard attacker who even outclassed Blaziken before it was given Speed Boost and a Mega Evolution. Slap a Choice Scarf on Infernape and he can be very prolific. Good Speed and Attack with an impressive movepool.
Empoleon's usage should only increase now that Fairy type has been introduced. I myself use Empoleon in VGC play because of its access to Icy Wind, Scald, Blizzard and Grass Knot. Great typing, pretty decent bulk and a good movepool. I chose Piplup because it was my starter in D/P and because of my own experiences with it in competitive.
As for Torterra, he got the short end of the stick (lol). Not much can be done with a Grass/Ground typing. The only starter with a double weakness (Ice) and has a handful of other common weaknesses. Yeah it has good bulk, but that doesn't matter when it has fairly bad typing. The Ground type does not save Torterra from its Grass weaknesses like Ground type did for Swampert.
If these three get eventual Mega Evolutions, Infernape will be most common, Empoleon might see some usage and for Torterra to do anything, it will need a boost like Venusaur did with its Mega Evo.