One thing that might help guide your decision are the shifters. Most IGHs are used with upright instead of drop bars so most shifters are designed accordingly. In other words most don't work well with drop bars. Sturmey Archer has a variety of shifters for their 3 speed hubs including one that can go one a down tube shifter boss. They have a bar end model too.
Because IGH shifting is so convenient when coasting or standing still, I find I like more than just a 3 speed. The joke about 3 speeds I heard on Ragbrai one time was "3 speed hub gearing, too high, too low and not quite right".