What class of service are you flying? If economy, what fare type?
BAEC drastically slashed earnings for economy fares this April.
Regular economy fares ("Low": K, L, M, N, S, V) were reduced to 50%, and the cheapest three ("Lowest") fare classes (Q, O, G) even to 25% of miles flown in earning Avios and TP.
With AA, all of those continue to earn 100%. You'd need to fly on expensive Y, B or H fares to earn 100% Avios and TP in BAEC.
This alone would lead me to credit all those flights to AA. With three annual LHR-RDU flights plus two Asian flights and some European ones you should *just* sneak past Platinum at 50,000 miles flown. That'd be impossible on BA with reduced tier point earning post-April devaluation.
As far as status and benefits conferred is concerned, AA Platinum or BA Silver is pretty much a wash. You'll enjoy pretty much the same benefits - you'd get access to the Galleries Club lounges at LHR either way, and can select seats on BA flights for free exactly the same as you can as a BA silver. As an AA status holder, I feel very well treated on and by BA.
Advantage of BA status when flying AA: You'd get lounge access on domestic AA itineraries.
Going to AA, you will lose the RFS redemption abilities for European flights, so when redeeming your Avios for those is your preferred thing, be prepared to pay more - those cost 10k miles plus BA's egregious charges when redeeming for intra-Europe flights on BA. And you will not be able to redeem AA miles for upgrades on BA flights (except travelling on very pricey Y/B fares). That's about the disdvantages I can think of... the far higher earnings should outweigh all this.
I would see that I'd get to Silver and continue to credit to BAEC for the rest of the year, and re-evaluate come next year January (AA uses calender years for status accrual purposes). As the writing is on the wall for a devaluation of AAdvantage, I`d wait that out before committing.
edit: While there is an AA co-branded credit card out there that does give status qualifying miles for spend (10,000 EQM for USD 40,000 in spend), that card (Citi AAdvantage Executive card, $450 annual fee) is only available to US residents. AA's UK-issued co-branded credit card does not award this. Too bad you're not living in Austria - the Airberlin/Niki card issued there grants one EQM for every Euro spent on it, even including cash advances.... spend 100k Euros on it and you're OW Emerald without flying
