If you go to Civitai now you'll find a slew of amazing looking sample images for each checkpoint. However, these are heavily prompt-engineered and cherry-picked of course, and there is no good "objective" way of comparing different checkpoints.
In an attempt to address this we've created Checkpoint Arena, a small hobbyist project to compare Stable Diffusion checkpoints across a set of uniform, standardized and simple prompts.
I personally find it very enjoyable to click through some of the different seeds (left/right arrow) on the compare page (https://checkpoint-arena.com/compare) to see how the different checkpoints can arrive at very-different-yet-similar-looking results!