I've never used bots that are voting in rounds because I want to have immediate results and don't have time to check the right moment for a transfer. @minnowbooster is the one I trust for many reasons. The most important for me is that I've never lost anything by using MB.

For the SP calculation (50%) the internal medium price is being used (currently ~ 4.89) but in most cases it doesn't make a big difference.

Edit:
You should take a look at https://www.minnowbooster.net (scroll down) to see the available SBD send ranges. Currently there is no strong vote available but that may change in the coming hours/days.

Last time I used MB, I received an upvote of ~ $46.00 for 20 SBD ;) Of course there is not much money to make with the vote alone but it can lead to more strong votes because the post may get the attention of other whales and if that's the case it has still a good ROI after curation. In bad cases you'll get ~ the amount back that you've sent to them.