Depends on the amount you are trying to invest. If you are talking about around 5000 or more worth of Steem Power then definitely go for Steem Power. However if you are only trying to invest around 500SP then personally I think you should go with SBD.
This might be an unpopular opinion to some but using bid-bots has his own set of upsides. If your articles/contents are at least of decent quality, then promoting them with bid-bots would surely yield some profits.
In case your article/contents are that not much great. At least you are still getting some SP from bid-bot vote. You might lose some cents but you have gained some visibility and followers which is more important long-term.