It all comes down to opinion for this context of question. But it is difficult to deny that something is abnormal about the sightings, and evidence. Exsanguinated goats and livestock, and a sighting on a police car camera, which are renowned for their near impossibility to doctor or edit. The sighting can be categorised into 2 classes. Class A would be the more ludicrous claims, of which all evidence has been proved a hoax. The quills, glowing red eyes, 20 foot leaps in a single bound. All of these characteristics could be pinned down to narcotics, mental illness. However Class B, the more believable of the 2, I would bet my left...well, I am 100% positive that Class B exists. The sightings seem to show the same consistency in characteristics.
Much like a hairless canine of a sort, with shorter front legs, and an elongated snout. As for the draining of the blood of livestock. That is yet to be determined. Once a chupacabra has been captured live, it can be studied. (humanely, I hope.) And answeres will come soon after.

As per therealdeal30's answer, i believe most of it started in Arizona south of Tucson down towards the border and moved eastword into southern New Mexico near Deming and Las Cruces, on into El Paso,TX area and all the way down the Rio Grande River in all the way to the Gulf Of Mexico in South Texas. Around Texas border towns such as Del Rio, Eagle Pass, the Big Bend Area, Laredo,McAllen,Brownsville and points north.

Here is a good link with some info, i don't know if it's the best info, but it says mainly it's origins are up for debate. From what I know it first appeared along the Texas/Mexico border and have been numerous reports for years regarding this possible creature and the odd livestock killings, not so much mutilations, but the blood was cleanly drained from them from a bite mark.

http://science.howstuffworks.com/chupacabra1.htm