Holger, check out this website
http://src.infinitewave.ca/ it was done recently through the aid of Dave Horrocks & some of the regular contributors from Gelnn Meadow's Mastering Webboard. It shows detailed passband & transition FFT's from the majority of SRC algorithms available today (both on the PC & the Mac) including Weiss Saracon, Barbabatch, Peak 5 etc.
Looking at the Passband & Transition samples, tells a good story of the quality of the SRC's on test. Not conclusive evidence, as usual it's always best to use your ears, so I created some test files (unmastered & mastered snippets of music) & the 96kHz test files were SRC'd through a lot of the available converters. These include - Peak 4, Pro Tools Tweakhead, Audition, R8Brain Free, Sequoia, Wavelab, Barbabatch plus a couple more.
During the listening tests I conducted before the test files were made official. I couldn't believe my ears when I actually preferred the conversion done by Barbabatch. It sounded truer to the original 44.1kHz source file then the Saracon conversion did. The Saracon still sounded great, but it had added a slight increase in the high frequencies, which was confirmed by Alan Silverman late with his own blind tests. He upsampled a 44.1k test file to 96k & then SRC'd back down to 44.1 using Weiss Saracon & managed to pick Saracon's conversion over the original 44.1kHz test 8 out of 10 times due to the slight boost in HF content.
For the testing I did, I compared how the SRC'd files sounded against the original source file & listened for differences, not so much comparing the SRC'd files against each other. I just found that to my ears the Barbabatch converted file sounded truer to the original source then Saracon did. I also did some null tests & found a lot of the SRC'd test files nulled perfectly against each other, such as Adobe Audition, Pro Tools Tweakhead, Barbabatch 4 & R8Brain Free. All of these files nulled against each other. The ones that didn't null perfectly included Wavelab's SRC, Seqoiua & Saracon. There were some dreadful ones too like Peak 4, Waveburner & Logic which was an eye opener.
If you'd like to hear the listening tests that I compiled with the help of Dave Horrocks for the mastering webboard you can still download it here (to my surprise as it's about 6 months old now)
http://www.iwserver2.com/LT.zip & the voting page is still up too
http://src.infinitewave.ca/VOTE/vote.phpI am still hoping that iZotope will release their 64bit SRC as a standalone application for Mac as well. Up till then I think I'll stick with Barbabatch 4 even though BB4 is only 32bit & minimum phase. I have made requests to Aram from Audioease to make BB 64bit internal processing with some more dither options & they said it will be considered for a future release, but it's been over 6 months since I made that request & nothing more has happened to my knowledge.
Hope this helps you with your future choice.
Matt