Colnago, de rosa imo are consistent winners for looks and performance. There are lots of other good brands too. Don't expect any miracles stiffness wise though. A lot of those frames have pretty light tubing. My SL colnago is rather flexy compared to my modern alu frame, but stiffer than many vintage steel frames ime. That said look up the video of saronni sprinting on his old colnago, it won't slow you down too badly