I normally put anyone who want to join Steem afresh through the Steemit.com interface, to me, I think it's the easiest and what they'll be dealing with as new comers instead of other interface.
Aside from that, I'll choose partiko too, for anyone who is conversant with facebook will surely find it easy and calm to comprehend when going @partiko app to create both an account and also enjoy an amazing yet familiarize similar experience.