Lets first look at the ideologies of both parties just in terms of immigrants.

Replubicans:

They have been traditionally conservative about this issue. They are totally against amnesty, and not that   sympathetic for immigrants. Don't believe me? Look at Mitt Romney. He is considered more conservative than anybody else. He is totally against amnesty or legalizing the undocumented immigrants by some legal process like paying taxes and learning English etc. You should have watched the Republican debate back in fall 2007 where he was so against Huckabee's idea of letting illegal immigrant's children to benefit from the education system of USA.

John McCain is considered a MAVERICK..someone who has at times went against his own party policies. That's when he went across the aisle and he and Tedd Kennedy ( Democrat) came up with the bill that would create a path to provide citizenship to all the undocumented immigrants but that bill died because of staunch disapproval from replubican politicians.

Replubican party has traditionally been unsympathetic to immigrants. Make no mistake or confusion about that.

Ironically, right now that McCain needs support from conservatives, he has been totally silent on this issue of amnesty bill. Coz if he does, he might lose the base support from his own party.

Democrtats:

Obama and Hillary have always been vocal support of legalizing all those illegal immigrants and let them come out of the shadow so that they aren't harrassed and exploited by the employers.

That's my understanding. So on the issue of increasing H1b quotas or legalizing illegals or being little bit more lenient in this issue I think democrats are the one to go for.

I might be wrong and never ashamed to be corrected if anyone can educate me more.