I'm assuming we're talking mechanical here and not Di2 or EPS.

I find that Shimano systems shift smoother across the board. Campy has a bit more CF bling and I find it to be a bit more serviceable in general. In terms of trim-level, I would rate Ultegra on par with Chorus. And I'd put Athena between 105 and Ultegra.

That said, I think the biggest thing you will want to be concerned with is how the shifting works and how the hoods feel. If you're used to Shimano's Dual-Control and don't relish a change or learning a new system then maybe go for Ultegra. But really learning to use Campy Ergo levers isn't a big deal. However, you do need to try them out to see if they fit nicely in your hands and you can reach all the controls from all your hand positions. Some people can't hit the thumb levers from the drops. For me, it was a bit of a stretch to do so. And although I ride primarily with Shimano systems and got used to Dual-Control, I've never been overly fond of it and liked Campy's way of operating the shifters better. Actually the decoupled shifting and braking was one of the reasons I upgraded to Di2. I liked the placement of the shifter buttons with Shimano but wanted to give up Dual-Control.

My suggestion to you would be to try riding a Campy-equipped bike to see if you like the ergonomics. Also don't forget SRAM... unless of course you've already ruled them out for one reason or another.