From what I read it will be the Lightning Network which is an ingenious solution to the Bitcoin scalability problem and has definite advantages:

• The transaction fees are tiny (currently 1 satoshi per transaction), which allows micro-payments.
• Transactions are almost instantaneous since their validation depends only on the latency time of the network. This is where the network - Lightning takes its name: payments are made at lightning speed.
• Transactions are much more confidential than transactions on the chain.