Ive ordered a 9551 but saw this ---- Futaba BLS571SV
is this any better?
Metalnut it is right, but I'll answer anyway.
The BLS571SV is the replacement for the BLS551. Both are slightly higher specification and featured than the 9551.
The 9551 uses a coreless motor instead of brushless and has marginally slower (0.10 vs 0.11) speed at 6V and torque specs that are within a bees proverbial.
BLS series = brushless.
Specs of the old 551 and new 571 are essentially identical (at the same voltage) except two keys things - it's s.bus compatible (program via PC) and can handle higher voltages. When using HV (not many 1/10th ESCs offer this yet) it does perform better on paper.
Is the 571 better? Yes, yes it is. But not by much in the grand scheme of things.
If you don't care about HV and s.bus and having a brushless motor (quieter, smoother, longer life, less power draw - usually) isn't imperative, the extra $$$$ wouldn't be worth it.
The 9551 is a very solid performer. The more expensive server won't make you faster.