I am building the Tamiya Williams FW24. Beautiful kit, as are all Tamiyas. Lots of detail, accuracy, and reasonably good fit.
My favorite race cars were the Watson roadsters, and I know they are popular with many model race car builders. Look at the value of the old AMT version and the Etzel one.
My dream is that someone would convince Tamiya to kit this car, say one of the AJ Foyt winners, with detail and accuracy of their current F1 models :-)