If your tapes are DV50, you should capture DV50.
1:1 is a waste of space and will not improve the picture, since the compression was already done in camera.
2:1 is probably degrading the image to a small degree as you are essentially double compressing everything.
There would be some benefit in capturing in 1:1 or 2:1 if you were shooting DV25, as that codec uses the inferior 4:1:1 color space….DV50 is 4:2:2, like the others.