Contrary to what most people may think, energy weapons aren't always the best choice. It takes a very sophisticated technology to create strong, long lasting energy source that could rival an easily designed explosive or high-piercing shell.
While energy weapons have a much higher damage potential, for smaller projectile weapons the effort really isn't worth it. Low level energy technology tends to be reserved for field related items like beam swords.
A basic Beta Zero Weapon
(B0W gun) fires only solid bullets but is a very common weapon. Its parts and ammo are quite inexpensive.
An agent's Sonic Gun, while more
damaging, is much more costly to recharge. Its parts are far more obscure and much tougher to obtain.
If you're not in the government, cost is DEFINITELY a factor!