I haven't compared the two but owned the Cary for a while. With stock tubes it's okay, but when I put in NOS Sylvanias the preamp really started to sing. The Cary house sound is very biased towards the mid-range, but this preamp delivered good bass, not outstanding, but very listenable. It is a bit warmer than other preamps I have heard. My current preamp, a Joule Electra LA-100 MkIII is more transparent and extends the frequency range better than the Cary.
It might be helpful to know what amp you're going to use it with. I used my SLP-98L with a Cary V12i and they mated very well. I would not say the Cary is a cut above the BAT. I believe if you get to hear them both the BAT will sound very different. It will depend on the sound you are looking for and the synergy with the rest of your system that will probably determine what is best for you. I have heard the SLP-98 Jaguar Red versions are better than the Black versions. Not sure why, maybe because the Jaguar Red ones are the most recent production. Also, mine did not have the Jensen oil cap upgrade or the other Cary upgrades that are available for the unit. These could make a difference in the sound.