I was in a very similar situation as you until last year, where the company I was working for was HQ'd in Atlanta, so I had a lot of flights to US destinations as well as international. I ended up having both SE and Platinum status on AC and Delta at the same time. As
Adam Smith said, it depends on where you flying, but here are my high level points for what they are worth:
1. I was reasonably successful at getting comp upgrades out of Toronto, on virtually any other flight between US destinations forget it except on the odd route even with Platinum, as even a lot of Diamonds don't get upgraded. That being said, and as others have noted, the fares for Business Class on Delta can be pretty reasonable if your company allows you to book a P fare.
2. I got really tired of connecting in Atlanta really fast, and ended up using direct AC flights wherever possible as it just wasn't worth the extra accumulated days in Hartsfield Jackson. I still get shudders thinking of the wasted hours in that f'ing airport.
3. Delta is a great airline, and I got used to flights being on time, and messages in advance when they are delayed, and even notices when bags were loaded on the plane. They are light years ahead of AC with their operations.