The assault class in my opinion is the most well rounded class. You have anti tank grenades dynamite and a rocket gun. All of which work on infantry too. So as you know as long as you are earning points you're earning overall rank as well as rank for your class. So PTFO! Conquest / operations is probably the best to earn rank as anyone near the flags get points for capturing the flag.
Assault rank is 50,000 points per rank. You can view your class rank in the customize screen during matches it's in the top left corner. You can also view it under the solider tab in the main menu. Go to soldier and click where it tells you best class and then you can select each class and view what your score is.