I have tried so many different op amps. The OPA627 is nice. The larger format PDIP "BP" version are the best version. The can "AM" versions are just too bright sounding. They are very clean and fast (when using a proper power supply and oscillation compensation), but they lack meaty bass. The SMD OPA827 is much better in this case. These are the two best monolithic "FET" op amps.
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In any case, the discrete op amps are highly superior to any of the monolothic version. However, you need to make sure you have an adequate power supply as these are all biased into Class A.
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The Sparkos Labs are very nice. They are bipolar and have a very clean sound. However, I have found that they "push too hard" on the signal and things become very harsh on the edge of sounds. Sparkos would be good if you have a very soft system.
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The Sonic Imagery 992/994 are about the best bipolar discrete op amps. Very clean, very clear and no harshness. Absolute transparency.
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Burson V6 Vivid are excellent and impart just a tiny bit of FET signature, but they are truly awsome.
