Spearow and Fearow - Recommended
Nidoran♀, Nidorina and Nidoqueen - Acceptable
Nidoran♂, Nidorino and Nidoking - Recommended
Red Version players can save time by catching two Nidoran♂s and trading one of them for a Nidoran♀ later in the game. The trade is available in Blue Version as well, but Nidoran♀ is more common anyway.
When you're done, go back to Viridian City and head north onto Route 2.