mix down file format

Just wanted to ask what is the best or preferred file format to mix down to burn to CD ? wave or flac ? and is there is difference in sound quality ? just wondering ?

Red Book CD is your safest bet.  See Sony, Sound Forge.  Comes w/ CD Architect.  So does the "cheap" Studio version, I think.
 
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If you're coming from 24 bit and especially if your track has quieter moments you may want to check out dithering.

For CD, you have no choice. It must be 44.1 KHz and 16 bits to satisfy the specification and be playable on CD players. This will tell you all about it.
 
For other formats, it depends on the software you use for encoding. FLAC encoders can handle any file format, including 32-bit floats and high sample rates, so if you're exporting for FLAC encoding leave the export file the same as your project (and don't dither).
 
MP3 encoders work best if you give them the highest-quality format they can handle. The most widely-used encoder, which is also used by SONAR, is the free open-source LAME. Some versions, like some other MP3 encoders, can't process 32-bit files, so you might need to export 24-bit files for them. Some encoders can't handle some sample rates, so if you're recording at 48 or 96 KHz, make sure the encoder you're using can deal with it. LAME can, I think. If you're recording at 192 KHz, just stop doing that. 
 
The most important factor when encoding to MP3 is not the source file format but rather the target bitrate. If file size is not an issue, encode to 320 kb/s. Keep in mind that many file-hosting sites automatically re-encode your MP3s to 128 kb/s for streaming, but that process will work better against a 320 kb/s source file than if you send a 128 kb/s file that doesn't need to be re-encoded. So always use the highest bitrate possible (you may have to compromise if a host site has a file size limit).
 
Somebody is likely to point out that you can't hear the difference between 320 and, say 192 kb/s. It's mostly true. You have to listen very closely to specific high-frequency elements to hear any difference. However, you don't know what might be subsequently done to your file, such as converting back to wave or re-encoding to a lower bitrate. 320 lets you keep the best quality possible for any further processing.

Thanks everyone ...

I think Flac was great back when Hard drives and storage was an issue, It saves about 25% of the file size and they do certainly sound good. But now we really shouldn't be worried about file size anymore. I like Flac for downloads if I'm going to play them on the computer. 
But- 
Flac won't play on most MP3 players and car stereo systems so MP3  is a little more universal. 
 
I stay with working from start to finish with 44.1 as my music is not going to sound any different at a higher clock rate. My studio is basic stuff so I'm happy with that. The songs even seem to sound about the same after I upload them to sound cloud, clicks or reverbnation. I upload at 160 KB because of my limited bandwidth. 

FWIW I'm always fond of pointing out that MP3 is not a data compression technology, it's a data omission technology.

I think the consensus from that 48/96 thread was that it may increase quality especially for softsynths that don't have an oversampling mode. So if your computer has no issues with the increased CPU load and file size it's a good default setting. However, 48 or even 44.1 is fine if your synths do have oversampling or if there is no difference for that synth. So "know what you've got" is a good rule of thumb I guess.

I have been considering switching to 48 too for the same reason Alex mentioned.

Yes and a lot of the Session drummer samples are flac

You mean those plugins benefit from a softsynth running at 96KHz? I remember there was also some discussion if the "mellower highs" weren't simply a result from SRC-induced LPFing.

I'd be interested to hear if you have specific plugins that work better at 96KHz.

Cool, I'll see if I can find it.