I bet to Totally agree with you on your choice, not because of favouritism or to be liked by you, but the truth of the matter is that those logos actually depicted what they are made for.
Bitcoin is now a trademark with the B boldly displayed on their logo. This has given bitcoin a very distinctive mark to the extent that you don't even need to look at the logo twice to know that it is bitcoin. So I think the logo is worth selecting.
The tau logo also depicted what it stands for. The letters were well designed and calved so well to attached to the next letter.
I must give kudos to the designer, that was really a display of ingenuity and high level of professionalism.
If were to vote, I would definitely go for both logos.