I personally prefer pure ammonia from ACE hardware. Ensure that is is pure though.
The reason for this is because you can measure the ammonia and add exactly what you want to raise the ammonia to a certain PPM. With a raw shrimp, it takes a good bit for the ammonia level to rise and it is a bit unpredictable where it will rise to or if it will rise enough to start a good cycle. Ammonia is ammonia so the source isn't too much of a concern, be it in a bottle or from a shrimp or even urine, yes some people use their own urine to start their cycle haha.
To ensure the bottled ammonia is pure, shake the bottle vigorously, if the bubbles disapate almost instantly, it's pure. If it foams, it has additives and should not be used.
One benefit to a shrimp though, most places just look at you weird and give you raw shrimp for free haha. My local Publix supermarket did that for me when I started the cycle on a small 10 gallon. I did use pure ammonia for my 75 gallon though.