I've done both for many years and could argue either side. Agree with True Grit on pricing. I'd take 2 truck loads of $300 steers with no spots!!
I can give you my exact steer numbers for last year. I bought heavy 4 and light 5 weights. I put them on native grasses, and other than a little cake on weekends to keep them coming in the lot, that's all they got. Bought them mid May and sold them 11-1. I did not do ear implants last year. Everyone dreams of 2lb a day gain, but without implants my steers averaged 1.32 adg. You can figure the profit based on your market. Based on my available grass, I can run a lot more 5 weight steers than cow calf pairs. However, I lose more and treat WAY more sickness in stockers than I do my own herd.
If you run maximum carrying capacity of both, I don't feel there's a huge difference in profit margin. My grandfather started his cattle business in 1916 and kept way more meticulous records than I do and he always told me the difference wasn't great enough to keep you from doing the one you enjoy most. That being said, I enjoy the pairs more and feel the work they cause is somewhat more enjoyable and they cause me personally less stress.