You can go wherever you'd like. You pay insurance so you can get your car fixed the way you want right?
The insurance companies just have deals with those body shops... the shop charges the ins. company a lower rate in exhange for the ins. company "recommending" their shop. The "guarentee" is moot, *any* shop should stand behind their work, if they don't then you don't want to go there.
I'd still recommend Shaber Ave Auto Body, since Bruce is the bomb, that guy knows his shit... he's been in the business at least 40 years. It might be too late tho, since insurance usually only gives you a check if you've agreed to one of their recommended shops, otherwise the write a check to you and the body shop. It's less hassle that way, but I don't know about the quality of those shops. Plus Shaver Ave is expensive... $1200 prolly wouldn't cover it!
Chances are, any of those shops will do a decent job, or they wouldn't be in business w/ the insurance company. I doubt AllState works with shady shops. I just figure, if my insurance is paying for it, get the best quality job available.