Delta is the most with-it of the big USA players right now if you're looking for a preferred airline with good domestic and international route networks, and I've had some good experiences with them going far beyond necessary for IRROPS recovery when my no-status self was flying cheap or award tickets. And I feel like they're trying to up their service game on international routes lately. As a 5'9" person married to a 6'2" person, I'm okay with paying extra for Comfort+, even if it's not a separate cabin situation. Your Leg Room Needs May Vary.

I'd rather connect in AMS than LHR too but wouldn't regard it as a huge deal-breaker either way.

BA still has a very good soft product in many ways, but I think their service recovery is often weak compared to the US options and one of the big down sides of the BA Avios program for me (in addition to high fuel surcharges on transatlantic flights) is that it's all segment-based so unless your home airport is a BA or American hub, you end up spending a fair number of miles just to get to your main flight.

If you're interested in status-chasing, there are a few AmEx Delta cards that offer Medallion-qualifying miles that let let you shortcut your way to status. I'm about to hit Silver based on one east coast round trip, one transatlantic trip, and the first half of a Florida-Portland, Oregon ticket and a whole bunch of home improvement spending ran through the Delta Platinum card. While a lot of people complain about the 'Sky Peso' and how many miles it takes to redeem for long haul premium cabins, Delta actually often has some sweet spots in terms of the number of miles needed for domestic coach redemptions and availability for a family of four.

Have a great trip!