Almost all the bidbots accept the delegation of steempower from investors in steem. Most of these bid bots give 13-15% returns. There are different websites which provide you with the statistics of ROI on delegated steem power.
Steemprofit.info provides a good statistics about the APR by different bots.
According to my experience, Smartsteem and Jerrybanfield are the two reputed bots who have delivered consistent returns on delegated steem power. However, if anyone is interested in comparative analysis one needs an account which delegates to many such bid bots.
TipU which is one such bot promotes their ROI to be one of the highest requests to check the account @wefund to understand ROI given by different bid bots on the delegated steem power.
It is not possible to identify one bot to be profitable as its ratio keeps on changing every time. One bot is profitable on one turn in the next turn it may end up in loss. Let’s assume a bot is giving upvote worth 1$ if it receives 2 bid of .1 $ each its vote will be distributed in the both bid in ration of .5$ each and both will end up in profitable. In the next round upvote worth is the same but if it receives bids valuing 1$ or more in next the bot will become in loss.
Considering above I will see which bot or bots are giving best profits in the round and will invest accordingly in two three or more bots.
Bots are not meant to be bring income instead they are meant to promote your post. Your friend is right most of the bots will end up you with loss. Let's say you used 1$ to get upvote from bid bot and you got 1.20 $ wort of upvote 25 % goes to curator and 75% goes to you. You redeem 50% of 75% as a spendable and 50% of it as a sp which will take 3 months to lock up.
Most bid bots will only rip you off and steal all the curation off of your post so that it leaves your followers with no returns in the from of curation rewards. I suggest a different way. Please work on your networking skills and you will be better off in the long run.