Highly scalable because of their centralized nature are Ripple (XRP) and Stellar (XLM), Stellar started as a Ripple fork. I finally went for Stellar because of the founder (he founded and sold MtGox and founded Ripple), more potential to grow because of lower cap, the complete feature set and some recent announcements (such as Kik/Kin moving from ETH to XLM, Singal-founder will use XLM for his MobileCoin).
I might buy Ripple after some correction though. Ripple has a different positioning but a good setup too. The cap is already very high, close to ETH's.
Edit: Why the downvote?
Edit2: changed that Stellar started as a Ripple fork