There are so many factors to consider including the inflation rate of dollars.

In the short term Steem Dollars will pay 10% APR interest which is good by banking standards, but poor by crypto standards.

STEEM is created at a rate of 100% APR, 90% of which is given to those with STEEM Power. STEEM Power is just STEEM that has been locked up with a 2 year vesting schedule. All else being equal, the market cap of Steem must double every year for the value of 1 STEEM to remain flat. Holding Steem Power is the best way to make a long-term play because you are protected from dilution anytime less than 90% of all STEEM is held as Steem Power.