Tough call - depends very much on where else you fly, but KLM business fares out of London are very good, and if you're regionally based then maybe even more so.

On the other hand, status on BA is hugely useful if you're doing an economy short haul every week on top; LHR-AMS-GVA would be an absolute pain in comparison, and I wouldn't much fancy doing LHR-AMS-ATL-anywhere in the US if I could fly direct.

If, on the other hand, you're regularly doing LHR-AMS-MNL, that's no worse than LHR-HKG-MNL on BA and probably a third of the price (as an example...) Would DL status and Virgin for transatlantic work better for you perhaps as well?