To get back to OP's question: Having had 4 babies under their auspices, and been closely involved with maternity services in both I would unhesitatingly say KINGS every time.
Tommies is OK, but the home-from-home is a bit dire (think 'nice hospital room' rather than anything more special - and definitely NOT a home-from-home), whereas the new midwife led rooms at Kings are just beautiful places to be - really lovely (think boutique spa-hotel) - well they are brand new so they should be I suppose?
The labour wards on both are... well labour wards, not a pin to chose between them, or the expertise of the staff who work there.
The postnatal at Kings is streets ahead of Tommies, particularly as there are no specific visiting hours for partners whereas there are at Tommies and I've known this create a very difficult start for some Tommies Mums, especially those who've had a Caesarean and need the extra help & support that their partners can offer, but the busy midwives can't (though I hear on the grapevine that Tommies are bowing to pressure and may be thinking about relaxing their pn ward rules a little?).
Plus Kings has a lot more case-loading midwifery teams that you can link into so you can get a named midwife to care for you throughout your pregnancy/ labour/ birth and after. Tommies only has a couple. And I really would urge you to try to get with a case-loading team for the gold standard in maternity care.
Unless you live on Tommies doorstep, or have to go there for medical reason then I'd always go for Kings. I appreciate it's just my personal opinion though. Congratulations OP and Good luck with whichever you chose. 