Holding Steem Dollar: give true interest.
Holding Steem Power is giving no true interest. You just get partly compensated for the 100% inflation of steem. From this 100% you get 90% back. In away with round about 5% ¨you¨ pay for curation rewards and 5% for post rewards. So if steem grows more then 10% each year and you hold your steem in steem power you win.