Advice - Shimano Ultegra 6800 Groupset vs Campagnolo Athena Carbon Groupset

It's just one of those things - it either matters to you or it doesn't . For me it doesn't feel right to have wheels saying Campagnolo matched to a Shimano gruppo. It doesn't really matter anymore as if you want Campag wheels that don't shout 'Campagnolo' you can get the equivalent Fulcrum version.

Both Ultegra and Athena are very good. As there is little to separate performance-wise, other more subjective factors come in to play...

I ride Campagnolo because I prefer how it looks.
I ride Campagnolo because I have to replace stuff less often than my Shimano riding pals
I ride Campagnolo because its what I used when I discovered that even Cat2 was likely to evade me and it reminds me of my yoof.
I ride Campagnolo because as much as I like sushi, I'm really a pasta lover at heart.

For me it is Campag all the way, I have ridden bikes with Shimano 1055 back in the 80/90's and it was ok but I did break a lot of things. Things like bottom bracket cups, axles, replaced several cranks and even a hub (well the bearing cups) with Campag CDA/ Record I never had any issues. I have recently started replacing my old record items for more modern parts, I found that as usual Campag build quality is second to none and you have to admit it looks so good. But it looks nicer and I actually like the clunky gear change as I find it a help for me to know I have changed gear, as I had to come away from the old levers on the down tube to them being on the brake levers.

Personally you want the silver groupset as it will stand out perfectly, you want everyone to know you have Campag on your bike.