I switched to a firm, road saddle.
I love commuting on my 80s steel road bike, but have been dreading the rides on my hybrid ('09 Trek 7.2 FX), which has fenders and is used when rain threatens. It always felt like there was wasted energy being sucked into the void on the hybrid, meanwhile the road bike was an efficient joy to ride. Furthermore, the saddle was very uncomfortable. It used to feel comfortable enough, but I think the discomfort began when I changed to a below-the-saddle trekking bar setup.
Today I switched out the thickly padded Specialized BG Rival mtb saddle for an 80s San Selle Marco. The difference was profound. I was hoping to simply get comfort, but my riding efficiency was dramatically improved. I suppose the mtb saddle was akin to riding with a suspension seatpost in a way, given that I bounced up and down on it a bit.
Note that I had previously switched to 700x28 tires.
Now, I won't be picking the Trek over my road bike commuter unless it might rain, but at least I can enjoy the Trek when I do take it out