Depends what source you're using now and want to use in the future. BDA opens a world of possibilities for digital sources.
On the other hand, if you're mostly listening to CDs and plan to keep on doing so (likely the case if you're asking the question), then a good CDP is a must. You can't just use any old CDP and expect to get perfect sound, even using digital outputs.
I have both a Rega Apollo CDP and a NAD 542 hooked up to a Bryston B100-DA via coax digital. Both CDPs sound much better via digital out using the B100's D/A converters, but there is an audible difference between the two. Especially with headphones on, I can distinguish between the two sources. The NAD has a slightler sharper edge and sounds a bit flatter, while the Apollo sounds a bit smoother, yet fuller and with more 'presence'.
I never expected to hear any difference using digital, but I discovered the difference just by accident when my wife played a CD in the NAD (she doesn't like the top-loading Apollo) that I had played earlier in the Apollo. I noticed the difference immediately and was surprised how it suddenly sounded harsher in the NAD.
The difference is slight, but discernible, and let's face it: we generally pay a lot of money for slight differences, because to audiophiles the difference is worth it.
But all that probably doesn't answer your question. If you're current CDP is very good, and/or you intend to put all your music on a digital server, then I'd go BDA. If you need to upgrade your CDP anyway, then I'd go BCD.