For those that are considering BA, there's one thing you have to take into consideration. There's a four sector minimum but once you advance to the next level, it resets again. The points don't reset but the minimum sectors do.

Taken from the BA website.

"To reach Bronze is easy. All you need to do is fly BA at least twice and earn 300 Tier Points or take a total of 25 BA flights. Whichever you do first will get you to Bronze.
For Silver, you need to fly BA at least four times and earn 600 Tier Points or take a total of 50 BA flights.
To get to Gold, you will need to fly BA at least four times and earn 1500 Tier Points.
BA flights are:
flights operated by British Airways, including franchises and BA CityFlyer
codeshare flights on other carriers with a BA flight number
flights operated by Iberia, including franchises, with an IB flight number
Reward flights and agency or industry discounted bookings do not qualify."


If you do a lot of flying to the EU or the occasional SIN-SYD flight, it shouldn't be a problem. If you're expecting to get Emerald flying once HKG-LHR-BRU and back to get the sector minimum requirements, you're in for a surprise.

I banked some flights with BAEC and realized later that I couldn't get it cause I don't fly to EU that often.