The class I have been using as of late:
Battle Rifle
BoltShot
Frags
Thruster Pack/Jet Pack
Mobility
Dexterity
Saying this class is good is an understatement. I have been playing this game since release (off and on mostly) and have experimented with many styles of play and control settings. This class is easily one of the most versatile, mobile, and hard-hitting classes I have used to date.
Use the Battle Rifle. Period. It is the perfect utility weapon and can take out about anyone if you can aim. It doesn't matter if it is Rumble Pit, Team Slayer, or Big Team. If you need another gun like a DMR for long ranges, you can likely kill someone that had one with this class and take it.
The BoltShot is your premier close-quarters option. Coupled with mobility and Dexterity, the BoltShot can hit fast and hard and reload again with ease. It is also good for those annoying AR bumrushers if you can't BR them.
Thruster Pack if you are playing Bumper Jumper, Jet Pack if you are playing Default, Recon, or Boxer. Those armor abilities give you unprecedented mobility and give you vast opportunities for escapes and kills not afforded to people without them. Promethean Vision is also viable, however it is more recommended for players that play matchmaking in a party on a team. For players like me that strictly search alone, you will want more mobility as opposed to knowing your opponent's exact position.
Frag Grenades because of the sheer versatility of them. You can always pick up more grenades off the map.
Mobility gives you unhindered sprint so you can take other players by surprise, get into a power position faster than anyone, or scramble when one-shot.