the easiest way is to read through the 'learn' section and look for articles on the web comparing them.

You can look up the spec differences at the company websites, or any number of places.

The glaring difference:
HSD is capable of propelling the vehicle purely on the electric motor up to a certain speed, and as long as the driver doesn't punch the throttle. This saves the gas engine from having to accelerate the car- removing the biggest efficiency killer of them all. Hence Toyota and Ford hybrids get better mileage in the city, where there is more stop/go and slow speed driving. The electric does not assist at highway speed at all.

IMA does not propel the vehicle; it can only ASSIST the gas engine when high acceleration or loads are called for. It will help at all speeds. Honda hybrids get the 'traditional' higher mpg for hwy driving.

A Toyota or Ford can drive around the neighborhood in 'stealth' mode- no engine noise, just electric. Honda's cannot do that.