I am going to Georgetown for the LLM, and am contemplating an academic career. Is the SJD the most logical choice for this, given that most US-trained law professors seem to have the JD rather than the SJD?

I am intending to specialize in WTO/international economic law/investment law and Georgetown is the best in this field. However I've heard that if one wants to teach in the US, then the JD is a better choice, particularly since many law profs in top US schools seem to have Harvard/Yale/Stanford/Columbia JDs.

I am from the UK so could of course go back there (or elsewhere in Europe) to teach, if I have the SJD (as it's equivalent to a European PhD). But if I want to enter the US law teaching market, which is better - SJD or JD?

SJD is not an alternative to JD as far I know. JD is necessary for every lawyers who wish to practice, while SJD is the same as PhD or DPhil in Europe. If you look ahead for an academic career, SDJ is your choice.

The best route to a prof job in the USA is to get your JD from Yale (or maybe Harvard or Stanford). The SJD is a gamble, especially in my view because you're from a common law jurisdiction. Take a look at some faculties at which you'd like to teach and see how many UK LLB/ USA SJD types there are; I would guess there aren't many.

as for the LLM (with very few exceptions), the SJD program is tailored on foreign-trained lawyers who want to gain deeper knowledge in a particular field of law. that being said, a SJD is not necessary to pursue an academic career in the US, although it may certainly help you in building your profile as a foreign scholar. As an alternative, you may think of undertaking a PhD program, although it would mean to gain such degree outside the US, for no PhD in law is available in the US (guess what, this is why the SJD program exists)