The gameplay of the Combat Rogue is very dynamic despite the fact that it doesn't have a "Proc", the energy regeneration is so high that it makes the gameplay very appealing. Basically you are not going to be bored because the Combat specialization is of an exceptional quality, the hybrid that can be used in all situations whether for single or multiple targets. The Assassination specialization is slightly more powerful than the Combat, but it is still viable.
Update 5.2 : The Combat Rogue receives a few nerfs, however it is still viable, we will note an up of 5%.
This is an approximate ranking of the performance of each Class/Specialization
As you can see above, the Combat specialization is ranked quite well, but don't worry too much about this table, it can vary a lot depending on your raid composition. You can easily be first, you just need to understand this specialization well.
Combat Rogue Guide - 5.2
MOP Dungeon Guide: The Temple of the Jade Serpent
Assassination Rogue Guide - 5.2
WoW Profession Guide: Alchemy Leveling Guide - Production
Retribution Paladin Guide - 5.2