Honestly, I've had a great time with almost all of the weapons in the beta. I'll usually place a longer ranged weapon like a Pulse Rifle or Scout Rifle in the energy slot, and then either a Hand Cannon, Sidearm, Auto Rifle or Submachinegun in the Kinetic weapon slot. You don't really have to do this, but I think it's better to have a long-ranged weapon in your Energy slot, since you don't really want to be dealing with super abilities up close. My favourite combination is the Omolon Pulse Rifle in the Energy slot, and the Better Devils Hand Cannon in the Kinetic slot.
The Power weapons have been working pretty well as well. I've used the Fusion Rifle, Shotgun, Sniper Rifle and Rocket Launcher so far, and they all felt really good and powerful within their assigned roles.
However, I AM ABSOLUTELY HATING THE GRENADE LAUNCHERS AT THE MOMENT. I've found them incredibly difficult to use for two reasons:
#1: The arc on the grenades is really difficult for me to predict, and the shots are hard to land.
#2: When you DO land said shots, it feels like they do hardly any damage to be worth it, and the average explosion radius is so small that it's not funny.
Do take those gripes with a grain of salt though. We've only gotten to use the Hakke Grenade Launcher so far, it could just be a bad example.
Has anyone gotten a Linear Fusion Rifle yet?