Your local electronics store has just started selling time machines, anywhere doors, and invisibility helmets. You can only afford one. Which of these do you buy, and why?

I can see it now, the door is opening
where to, I wonder, would I want to go?
Into the past to see old London,
or maybe the Great Wall, or Mexico
dare I change the course of history
with this wonderful gift of time
or do I simply watch it all happen
changing none of the reason nor the rhyme
of events of the past as I’ve read them
in all of my history books,
of people who’ve lived and died before me
princes, paupers, and crooks.
And so I ponder such questions
wondering where in time I shall go
If I can, maybe bring a smile to those who need one
If only I can, tell them the things I already know
of who lives, who dies,
who kills and terrifies
of who prays and cries,
devil or angel in disguise?
So step in through the doors of time
and take this adventure with me –
Where would you like to go?
Or would you rather stay and just be?

Daily Prompt