Which test you use should depend on 1) what you want to use it for,2) what your child's strengths are (different tests test different things) and 3)what the organizations that will be seeing the scores accept and what their cut-offs are. So do some research.

One caution about the SB5 is that the newer tests produce lower scores. See Hoagies http://www.hoagiesgifted.org/highly_profoundly.htm
Unfortunately, since these tests are new, it seems to be not totally clear how the scores correlate with the scores on the older tests. Some folks are suggesting that the cut-off's for gifted and highly gifted be moved downward for children assessed on the new tests. Here's our experience: DS took the SB5 and got a FSIQ that fell in the profoundly gifted range according to the Hoagies table (and Deborah Ruf's book, Losing our Minds) but under the 145 cut-off for highly gifted which was used for the older tests. We have found that some organizations continue to use the older cut-offs and are not readily willing to accept lower scores on the new test. DS's scores answered the questions we needed answered for our own purposes, but it has been a little more difficult to advocate with them. This is not a problem with the test itself, just that people are not totally used to it yet.

Here are a couple articles I wish had been available when we were making our decision: http://www.gifteddevelopment.com/About_GDC/newiqtests.htm and http://www.davidsongifted.org/db/Articles_id_10405.aspx

I hope this is helpful.