I would definitely get the 8 1/2 fret. When I capo on the 3rd fret to play in the key of G, I see the 8 1/2 fret is like the 6th fret if I'm playing in D. This way it helps me to play the same chord shapes as if I'm playing in D. For example in D 0 6 5 is the 4th chord (G major) when capo up to 3rd fret. 0 8.5 7 is also the 4th chord (C major). Hope this makes sense.
updated by @wayne-jiang: 01/18/17 07:12:59PM