If you have enough gps traces to confirm the alignment of the bing and the bing is of good quality in your area then I would use bing. have a look at past questions by doing a search for questions such as this one http://help.openstreetmap.org/questions/6385/alignment-of-track-vs-background-imagery one way to get some good fixes with your GPS is to stay still for a while or to sit on park bench, which I can see on bing in my area, the trace will record a blob of points,an average,so do this at a few locations and it should give a good fix. here's how to draw buildings http://wiki.openstreetmap.org/wiki/Roof_modelling#Drawing_of_building_outlines_based_on_low_resolution_aerial_images

If you have enough gps traces to confirm the alignment of the bing and the bing is of good quality in your area then I would use bing. have a look at past questions by doing a search for questions such as this one http://help.openstreetmap.org/questions/6385/alignment-of-track-vs-background-imageryhttp://help.openstreetmap.org/questions/6385/alignment-of-track-vs-background-imagery one way to get some good fixes with your GPS is to stay still for a while or to sit on park bench, which I can see in my area, the trace will record a blob of points,an average,so do this at a few locations and it should give a good fix. here's how to draw buildings http://wiki.openstreetmap.org/wiki/Roof_modelling#Drawing_of_building_outlines_based_on_low_resolution_aerial_images

If you have enough gps traces to confirm the alignment of the bing and the bing is of good quality in your area then I would use bing. have a look at past questions by doing a search for questions such as this one http://help.openstreetmap.org/questions/6385/alignment-of-track-vs-background-imagery