Being based in MAN, the logical program would be BA. There's really no other OW option from there, so you'll sit on their planes a lot.
You will need to achieve silver (OW sapphire) for lounge access, which you'd need to earn 600 tier points for. One MAN-LHR-CDG/ZRH return will now only award you 20 of them (five for each segment, earnings halved compared to pre-April 28!) when booked in the lowest three fare buckets, so you''ll get to Silver after 30 return flights or 60 segments - the same as qualifying for Silver on Airberlin with 60 segments.
AA would let you qualify after 50 segments, but seeing you say you aren't flying to the US they are out due to their four flights on AA metal requirement.

Tip: Apply for a status match with AB leveraging your FB status. They'll likely match it to Gold, so you'll get a head start on enjoying the BA lounges . BA doesn't do this normally.

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