My harbor strategy is to place one or both of my original placements near harbors ... with the plans of making my first new settlement in a harbor -- preferably in a spot that borders the harbor and two hexes.
In my experience you particularly need a better trading ratio early in the game, when resources (both yours and others) are scarce, but I agree with those that suggest not placing either of your original settlements on a harbor.
A secondary benefit of putting your original placements near a harbor is that it prevents you from being boxed in, as it is usually easy to continue expanding around the edges of the board, settling on places that didn't look good for your original settlement, but are not at all bad later in the game.
Whether I use 3-1 or 2-1 harbors depends of course on which hexes I place my original settlements on, and whether I can reach the 2-1 that is most beneficial.
Some of my best games have been when I am heavily invested in a certain resource, and have the 2-1 port in that resource. (Because if I'm getting most of the wood, I can often get 1-1 trades with wood-deprived competitors first, then fall back on the 2-1 when necessary.)