We've stayed BC CL, but our GF experience is only RPC. I'll throw in our two cents, but Erika could provide a more direct comparison.
CR Atrium Club didn't feel crowded to me in the least. I think the large windows overlooking MK and the balcony space gave it a less crowded feel. Even when the lounge was "full" it didn't feel like we were on top of other guests, and the food area was never crowded during our stay. I'd probably rank the food offerings at CR pretty low compared to other CLs, so replenishing wasn't as much of an issue because it seemed like fewer options were available in the first place. But I thought the lounge was extremely comfortable and, at least during our stay, other guests were among the best we've encountered in terms of not monopolizing particular seats, etc. The CMs were really friendly, but not hovering. We've stayed CL at BC, GF RPC, Poly, BWI, AKL and CR. Of those, CR ranks one of the highest for lounge comfort and atmosphere.