First of all congratulations for having received admits from top MiM schools like HEC and LBS.
While you are aware that HEC ranks out LBS in FT rankings, the choice between the two totally depends on your goals and budget. However, there are a couple of factors that you should consider before making a decision. So, to give you an idea of both the schools, here is an overview:
HEC’s MiM program is 18-month long with an option of a gap year while LBS offers MiM program for a duration of 12-months which means you will be able to graduate sooner via LBS. However, at HEC you can have more time to hone up your knowledge which can benefit you later.
Post HEC program, if you are looking to end up in PE roles, you need to be fluent in French. At LBS, of course English is the first language so that will not be a problem for you.
Also, both the schools have excellent post-graduate opportunities. Both HEC and LBS have a placement rate of 96%. The average salary offered at HEC is 63,000 Euros while LBS offers an average salary of £42,183.
So, both the schools are good options and taking an admit in either is a pretty good investment and no matter what option you choose, it will definitely add value to your profile.
On a personal note, if you are open to learning French I would recommend HEC as the school enjoys a Harvard-like status for its MiM program. But if you are not open to learning French upto a B2 level of proficiency, LBS is the way to go.