By "law" do you mean the taught courses that the faculties offer, or the research profiles of the two faculties?
I will deal with each in turn:
To restate one of my earlier posts: the main difference in the undergraduate degrees is the structure which is remarkably different, the Oxford system consists of 3 papers taken for Mods at the end of the second term and all of the other exams at the end of the third year; with Cambridge 4 exams are taken at the end of the first year and then 5 a year thereafter. With Oxford Administrative Law and Jurisprudence are compulsory- neither are compulsory at Cambridge; the Cambridge system also means you take two extra subjects than your Oxford counterparts- in effect you get 4 extra choices which your Oxford counterparts will not get which can be taken from a wide range of subjects. For Cambridge Roman Law is still compulsory in the first year, whereas Oxford gives you a choice between Roman Law and Introduction to Law. Although personally I would take Roman Law- the subject is fascinating and gives you a good overview about how different areas of law interact.
Cambridge supervisions for each subject run for three terms whereas Oxford tutorials in each subject tend to run for one term but be considerably more frequent during that term.
I am told that Oxford is more theoretical and Cambridge is more black letter- I am yet to conclude on this myself, since taking Cambridge as an example there are a considerable number of Oxford educated lecturers and vice versa; some have taught at both institutions. Although from what I have seen essay questions are more common on Oxford law papers than on Cambridge ones which tend to have more problem questions.
Given the choice I would take the Cambridge law Tripos for undergraduate studies- ultimately it gives you more choice in choosing your options, so you can take a greater number of subjects thus having a wider range of subject knowledge after your BA. That said the Oxford structure does provide for greater time to reflect upon the subjects taken.
I do however believe that the Oxford BCL has the edge for postgraduate studies, it is an excellent course (but considerably hard work), which unlike many other courses (including the Cambridge LLM) is taught by lectures, seminars and tutorials. It is also longer course than the LLM, however if you wanted to specialise in PIL the LLM might be more appropriate (see below).
As for the research profiles both Faculties have their differing strengths, Cambridge has undoubtedly a better reputation in the field of Legal History than Oxford, and also is traditionally strong in Public International Law. Oxford has an excellent reputation for jurisprudence and private law (particularly restitution and conflicts). These factors are however of little concern to the aspiring undergraduate and are far more relevant to PhDs/DPhils.