Of course everybody knows about the Alien Blaster, but acknowledge that other Alien weapons are extremely powerful too!
Alien Desintegrators are ideal to kill powerful enemies, such as the Deathclaw. They have good accuracy and high durability.
The Alien Atomizer is also very powerful and useful. It is more powerful than the Plasma Pistol or any other Laser Pistol, such as Colonel Autumn's Laser Pistol.
The thing is, when you're out in the Wastes, you need to know where to refill your ammo! Buying more ammo for Energy and Small Guns weapons is easy - talk to any merchant which sells weapons (Flak and Shrapnel, in Rivet City for sure). Now, buying ammo for Alien weapons is more complex but easy to accomplish.
First of all, you need to complete Mothership Zeta (but remember to acquire the Alien Blaster found in the crash site!). After doing that, every 24 hours, Sally (the girl with whom you complete the quest) will give you a random Alien thing. She may give you ammo, weapons...etc.
In other words, to make sure you never run out of Alien ammo, visit Sally constantly and make sure after you've completed Mothership Zeta you pick up some Alien weapons and store them in your residence.