Second Kitz. The B10D is the cheaper made one. The B10A like the 8x24 series has an integrated common mode noise suppression filter, and that is perhaps why they do so well, but the B10D doesn't.
Now this all comes back to what's been reiterated many, many times, there is no one modem you can say is the best for everyone, and no one can design one that is.
The common mode noise filter is essentially a long length of coiled wire, so this is the equivalent of extending your phone line distance, so it may drop your attenuation a little. If your line already has such a filter (perhaps in the NTE faceplate or ADSL filter) that is doing a good job already at removing noise, or you don't have much noise on the line the filter is designed for, this additional filter may cause you to see a slightly lower sync rate without any benefit, especially on your long lines and already low sync rate.
You will only know if you buy and try both, even then out of your 3 or 4 lines, a filtered version may work better on one line and not the other, so you might need a mixture, and will you gain anything worth the effort and expense, I personally don't think so, but ultimately if you have the time and money to try that's your call of course.