Asusming you want a classic road racing machine, without hesitation:
Peugeot PX-10, c. 1967-1974, white Peugeot-BP livery
Pure racing heritage: Pingeon, Simpson, Merckx, Thevenet. Winner of the '67 TdF. Great cycling kit (the Peugeot-BP Team had probably the most iconic classic "look" of them all) Super ride, light and fast: a racing bike you can ride all day. Fast. Readily available in all frame sizes (top is long so choose accordingly) Classic components: Stronglight, Simplex, Mafac, Mavic Ample spare parts (except those skewers the Japanese horde like nothing else) Usually found in good condition: excellent topcoating, far better quality paint than Italian machines and amazingly durable chromium plating Cheap: eBay, Craigslist, local thrift stores.
Peter Kohler
Washington DC USA