I've been using a BDDI for a couple of weeks now and I'm totally, totally in love with the thing, with the caveat that you've got to spend lots of time with the controls to find "that sound." But once you find it, you'll be a BDDI junkie just like me. I can take my bass and the BDDI and plug into any power amp anywhere and have it sound like a just-retubed Bassman 100 -- but with far more tightness and authority.
For me, it was a choice between the BDDI and the Line 6, but I went with the BDDI based on a shedload of online reviews. To be fair to the Line 6, since I've never played though one, I have NO reason to suspect I'd not prefer it over the Sansamp. But the BDDI is what I bought, and I love it.
Somewhere in the Effects forum you'll see a thread I started about BDDI familiarization time; it may help you dial in your sound, maybe not. I'm still using more or less the same settings. Bass and drive up maybe just a tiny bit from what I stated, but still not at 12 o'clock.
Hope this helps.