Aren't they all the problem?
Actually, I don't think so. The U.S. can manage a small illegal immigrant population, and in fact must since a perfect system would strangle out liberty. What you must realize is that each group comes here differently and must be handled as separate problems. Hispanics can walk over the southern border into the country and are encouraged to do so by their government and by the corruption of officials in their countries. Canadians can also walk across the border, but have less reason to do so. Asians and Europeans fly to airports far from any border with visas that allow them to stay and/or work in the country.
The thing is, when you have an illegal alien problem, you need to look at what is lacking in law enforcement. Is it a visa overstay problem, a southern border problem, a northern border problem, or a problem with the naturalization process? If it's 4% a northern border problem, 6% a visa problem, 15% a naturalization process problem, and 75% a southern border problem, then the real problem is the southern border.