I strongly favor a 3-tooth drop between the two (outer) chainrings, because this works so well ratiometrically with a 2-tooth progression back. One of the all-time classic combinations is:
49-46 / 14-16-18-20-23 -- plug that into an Excel and you will see why I like it so well. I took the concept a step further in the mid 1970s with my third-step gearing: 49-46-43 / 13-16-19-23-26, which provides a beautiful set of 14 ratios if one avoids large-large cross-chaining.
In the 1970s I geared my Nishiki with a 50-47 / 14-16-18-20-23 half-step, which I could change in 5 minutes to a 50-42 / 14-16-18-20-23 1.5-step for rides in the hills.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069