Sorry about this, but I am going to be blunt.
It does NOT matter which mathematics modules you take. There is NO difference in the abilities gained that will be relevant to a prospective lawyer.
As a student; perhaps, but not as a lawyer. You will find that you will forget what you learned in either module within a matter of months anyway; the abilities will become lost. What davros said was merely speculation; and I think you'll find that the skills gained in a S1 or S2 module are not going to be of any significance to your legal career.
I also believe that you are asking for trouble by attempting to judge the mathematics modules worth. Mathematics is one of the hardest, if not the hardest A level. You only have to look at the number of exceptional students getting appalling marks within individual modules to see that. There is a huge disparity in the marks of modules; and much of what causes this is a lack of ability or understanding of a particular type of mathematics.
My friend managed to gain marks of 91%, 87% and 61% his AS level. He managed to score the 61% in statistics, as he admits, because he is less able at it.
Look. By far the most important thing is that you get the highest grade possible in your mathematics. You might struggle at statistics; many do (people are willing, in further maths, do take up to M5 to avoid doing statistics modules), and by pressurising yourself to take it because you believe it might be more useful may lead you to neglect the possibility of getting high grades in a different module.
Take what you enjoy, NOT what you think is best for your career. It is most advantageous to achieve highly.
Besides; you probably won't get a choice of modules in the first year, so this discussion has probably been a waste of time. Decide after you take an applied module whether you like it or not.
The debate as to whether mathematics is useful for law certainly is a minor issue enough. The debate as to what types of mathematics are useful for law is completely worthless.