While inviting people for meetings, do you prefer communication through e-mail or formal letter? why?

Firstly create appointment via email/letter then for quick response also make a call or F2F information 

Thanks for the invitation. I would prefer email. easier and faster to communicate.

Thanks for invitation,

I do prefer "e-mail", to save time and effort.

Now a days technology is the main vehicle to reach out people we want to communicate. But to ensure that your invitation landed to the hand of  people you want to invite, I prefer formal letter. For this both parties  has a chance for further query and directly collect responses from the people you would like to invite.

Thank you for the invitation.

Of course i prefer the e-mail, because it is faster.

I would certainly prefer Email. less time taking and professional.

Thanks 

An e-mail is more inclusive and reachable , that what I prefer