R, your price range might be a better way to figure out where you would like to be. As far as next to the LIRR, every time I am on a train and pass those buildings, I wonder how the tennants can take it. I wouldn't recommend it because the buildings are older, and I can't believe that you wouldn't hear the noise. Because that line is between the city and Jamaica, I am sure that the number of trains going by both day and night would be more than you would want to hear.
As far as north or south of Queens Blvd., I think it's really east or west, and I don't think it makes that much difference, although obviously there are more buildings that are closer to the rr when you are west of Queens Blvd.
East of Queens Blvd. there are plenty of building on 108th Street or Yellowstone, and they are in all kinds of price ranges, depending on ammenities. If you want to try to figure out what price range you need to stay in, feel free to contact me and I will pre-qualify you.