In the flac logfile i get this:

What does that bitrate signifies? Is higher better? Is lower (like 128KBit\s) worse?

You can't set a bitrate for FLAC as it is a lossless codec; these are VBR by nature and only allow you to "choose" the average bitrate by means of applying different complexities of compression. Regardless, EAC's bitrate selector will not apply, as you are using a User Defined Encoder. In effect, the bitrate in this situation means nothing.

Ok, so if i understood correctly, that bitrate in the log is EACs bitrate and it dosen't matter, because i'm using flac as an encoder, right?

You are essentially correct. The bitrate setting would only have an effect if the user chose one of the "predefined" parameter passing schemes. Many of these seem to be for outdated or uncommon encoders or settings thereof and custom command lines may be recommended instead.