I own bikes with both AXS (Force, disc) and Chorus (rim). Long post warning: TL/DR - probably go with Chorus.
AXS is great under the gun. Exactly why is hard to say, but I at least (and others have said the same) am more willing to make lots of little shifts with electronic to maintain the best cadence, rather than forcing a gear or over-spinning. It’s also great when tired at the end of a long ride. The AXS gear ratios make a lot of sense for most of us, too. 46/33 and 10-33 is pretty much perfect for anyone who isn’t appreciably north of 4w/kg. The shift ergonomics are idiot-proof, and great in gloves. Rival offers a great value PM option, and the app gives you some very cool data if that’s your thing. Electronic also gives you access to compensating and sequential modes, which I don’t like, but some people do.
On the other hand, the front shifting is not 100% reliable; I still get chain drop every 250-300km and no amount of fettling (by me or other mechanics) has ever totally resolved it. This is a topic of great debate on various forums: there are those who will swear blind it’s all in the setup, while others maintain it’s just pot luck and some units just suck. I’m in the latter camp, but don’t want to debate it in this thread. The disc brakes are also very fragile, in the sense that if you so much as look at them wrong, they will need a rebleed. The rim brakes lacked power when I tried them a few years back. Finally, it’s heavy (though weight is an overrated metric).
Chorus, like all mechanical Campag, shifts wonderfully when it’s set up well. It cannot be beaten for sound and feel IMO. The shape of the levers and hoods is the best on the market for me. The thumb shifters are rather love-them-or-hate-them, but if you like them, together with the ability to drop down multiple cogs with a single movement, you will think twice about having any other groupset on the bike. It’s not heavy, either. Aesthetics are personal but I really like it. The standard dual pivot brakes offer decent power which is adequate for my use case, but they won’t match discs. Last, it has no battery to charge and has a very analogue feel, which I like, but I acknowledge it’s personal.
But 12sp Campag mechanical is notoriously finicky to set up; if you have a bike with complex internal routing, I’d possibly advise against; you may never quite dial it in. Likewise, your mech hanger had better be perfectly straight. Be prepared to fettle a bit more often than you might like if you put significant mileage in. Spares are expensive, too, as you probably know, and be aware that your wheel options will be a bit more limited, though as you already have Campag wheels, that’s less of an issue. Some smart trainers don’t like Campag 12 speed, so research that if you’re planning to use the bike on a trainer (though apparently AXS cassettes play nicely enough for it to work)
As for your alternatives, mechanical Ultegra is competent and easy to live with but dull, possibly now obsolete, and I don’t like my brake levers moving side to side. If you’re going down that route, I’d have 105; it’s 95% as good and 1/3 cheaper. Di2 is great: objectively speaking, it probably does its key jobs better than anything else, but it’s very much at a higher price point. I still think the buttons are too small and close together, though, and it lacks a bit of charisma/feel. SRAM mechanical is definitely obsolete so I wouldn’t put any money (beyond routine maintenance) into that in 2022, personally.
Overall, and speaking personally:
- for a performance road bike or TT bike I’d go Di2, because it’s the most reliable and probably the best at its core job.
- for a winter or crit bike I’d go 105. It’s perfectly competent and not expensive, so if it breaks it’s not as big a deal.
- I’m reluctant to recommend Rival AXS because I don’t think you can totally trust the front shifting. But if yours stays dialled in, it’s ‘set and forget’, which is the biggest benefit of electronic outside of TTing.
- for most general riding, I’d go with Chorus. It looks and feels great, and is fairly sensibly priced. Just be prepared for a little more maintenance and DON’T cheap out on cables!