So the best way to actually grow is to just keep it in your wallet and not to invest any where.
Holding is a good way to earn bitcoin without any effort.But I don't think anyone will get profit for holding bitcoin.Because bitcoin is on a stable position now and none can guess what will happen to next.I will suggest to buy bitcoin when it's price goes to under 500$ atleast.And I don't think its the best way because you need a huge capital and so many times.rather I will choose investing on ICO as great way of earning bitcoin.
Holding bitcoins will maximize your profits in future only if the price of bitcoins goes higher then the purchase you made but it will never grow your coins as the number of bitcoins will be the same and it will not go to the next level if you simply hold them the best way to grow your coins is by putting them into trading.