I would go with the US segments. Their business product is really pretty good and certainly on par with Air Berlin (if not better, frankly). I'd definitely say the upside to a US award is the lower fees compared to IB. AB fees are also very reasonable. Downside to US is the lounges, which are somewhat meh, but compared to an Admiral's Club it's not a big step down.

I'm not a massive fan of AB since their connections in TXL are sort of a pain and intra-EU are Y-only.