I've had a brief (maybe 20-30 shots) look with the Larue mount and I've owned a couple of ARMS mounts with a #19S that I have been using a lot for about a year now.
Both the Larue and ARMS mounts are solid and have excellent return to zero qualities. I can't tell the difference between a 5-shot group fired all at aonce and a five shot-group where the mount has been removed after every shot with either mount.
The major difference between them I noticed is that ARMS uses a pad that relies heavily on both the ARMS mount and 1913 rail being in-spec to work and Larue uses an adjustable tensioning screw for its throw levers that allows you to fit it to the cheaper rails that aren't quite up to 1913 specs.
Over time, there is less tension on the ARMS mount from repeated locking and unlocking of the levers; but so far the zero hasn't shifted even a fraction and it still has perfect return to zero ability for me. However, the change in tension makes me wonder how much wear is happening with the pad on the ARMS mount and whether an adjustable tension throw lever might not have an advantage in longevity? However, the ARMS throw levers have been around for awhile now and I've yet to see complaints about their longevity.
For me, if I was buying a new mount, the main factors would be price, followed by how closely I thought my upper receiver matched the 1913 spec.