As others have said, you have to consider controls and ergonomics as well as sensor quality. The 50D is an old sensor design, and it shows it in terms of noise at higher ISOs. Some of the newer Rebels may be a bit better in that respect, but I have never used any of them. I much prefer the controls of the 50D.
I can tell you that despite jaomul's experience, I have found that the 50D can produce beautiful images at ISO 100 and 200. I have a lot of 50D prints hanging on walls, my own and others'. I have a 5D3 as well, and I still use the 50D for much of my macro work (to get the higher pixel density). I could post examples here, but the fact is that the low resolution of images on screen won't tell you much.