Definitely would go with Oman J as well. I find the service outstanding and catering better than BA F. The flight times also make it a much more comfortable journey and the BA routing seems too tiring. Have used to J lounge in BKK and MCT, and they are both great. BKK lounge has excellent staff and great food as well as Chandon which is great for BKK standards as the tax on champagne in Thailand is too high. The staff in both lounges are great and the new terminal at MCT is surprisingly ultra-luxe and a breeze to connect through, especially in J. Even so, the price is really too good to pass up. You could even look at upgrading the LHR leg to F which features the new product. I flew it recently and was truly blown away, it really is so much nicer in person than the photos.