As they said a long time ago on SNL: "Jane, you ignorant s..t"!
You posted: "I'm comparing Rasmussen to other pollsters. Sure they ask different populations. It's just that Rasmussen seems to select (ha ha) a population which gives the appearance (ha ha) that the conservative candidate or position is more favorable than what other pollsters find."
Rasmussen has always "selected" likely voters as their polling population. That IS their poll! I imagine they've alwiays polled that population because they understand that that population actually are the ones that vote and elect people!!!
At the present time, that population leans to and favors the right rather than the left. It hasn't always been that way. Rasmussen just reports. Why do you feel the need to display your stupidity?
You posted: "In a lot of, if not most, cases they're not prdicting outcomes but giving opinions of trends or what is happening at a particular momoent."
Look, Einstein, it doesn't matter what the opinions of the likely voters are right now, other than as a measure predicting what will happen on the day they vote! That's what we are observing in a Rasmussen poll, "LIKELY VOTERS". The current opinion on any particular day is ephemeral. You have to look at the trends in order to know what will likely happen. That's what Rasmussen does!
The accuracy of All polls are judged by the outcomes of elections!. Elections are the only true measure we have to judge the accuracy of any poll. Elections are the "big" state run poll! There is no other true measure. Rasmussen is one of the most accurate in predicting outcomes of elections.
From Fordham University: http://www.fordham.edu/images/academics/graduate_schools/gsas/elections_and_campaign_/poll%20accuracy%20in%20the%202008%20presidential%20election.pdf