Off the top of my head (kaka please confirm):
Amex (except CX Amex and Centurion): $7.5/mile for first $160,000 spending/year, $100 per 8,000 miles (120,000MR) converted plus $240 annual Turbo Reward fee (except Plat Charge but including Plat Credit)
Dah Sing BA: $6/mile, no fee
HSBC Premier: $2.78/mile on your 6X category ($16.67/mile otherwise), $300 fee for 1 year's worth of conversions.

Note with HSBC Premier - I believe your Rewardcash can come out of any card (e.g. the Unionpays), but you must be Premier to enable conversion to Avios.

Advantage with having HSBC over Dah Sing and Amex is HSBC has far more Rewardcash promotions (e.g. Times Square/NTP Red Hot Festival 15X, Mannings 40X) than the other two.