Let's see now, there were U33Bs (ordered by NYC), SD45s (ordered by PRR), GP40s (ordered by NYC), and U23Bs, U23Cs, GP38s, SD38s, SW1500s, GP38-2s (all ordered by PC) -- just to name a few.
In later years (post bust) everything brought on the property new was low in HP (and of course, price). The GP38 and GP38-2 units probably were the best overall investment -- providing outstanding service for many years thereafter. They were ideal for local switcher service, but not enough "oomph" to get any speed up on main lines, and the dynamic brakes were useless. Of course, there were so many slow orders, it hardly mattered!
At one point, some of these lower HP units (along with the GE counterpart U23B) were specified by PC as long hood lead units. They were not popular with crews as lead units in consists.