So should I make my assault troops carry a shotgun or assault rifle? I find shotgun way too situational at lower levels.
I always leave them with a shotgun at early levels, but I basically use them exclusively as Run and Gun flankers. One of their big advantages is that they basically get one of their most important skills in Run and Gun the instant they hit Squaddie, and they can make the best use of it with a shotgun.
I switch mine to the rifle equivalent with every new weapon tier during the time where the rifle is available but I'm still researching the shotgun upgrade, but outside that interim period it's all shotguns all the time.