It depends what you want to gen and what prompting style you prefer.
I have found SD 1.5/6 to be far more flexible than SDXL. SDXL seems more „neutered“ and biased towards a specific style (like dalle/midj); but this may change as people train more diverse checkpoints and loras for SDXL.
This is a interesting statement, as Stable Diffusion XL implementations vary from "worse than SD 1.5" to "Competitive with DALL-E 3."