American Express Membership Rewards - UK Amex PRG vs bmi Amex Card - Comparison for Earning Points/Miles

I'm new to MR points, so hoping you guys can help. I have a Preferred Rewards Gold card and a (regular) bmi Amex card (both UK cards). I am wondering which one to make my primary (only?) Amex card for spending.

So far I am thinking:
Amex PRG:
+ 2 MR points for each £ on shopping for travel or at supermarkets (until Jan 2013)
- 1 MR point for each £ elsewhere
- Transfer to Avios is 1:1 (except for promotions, which I've read here are very rare)
+ MR points are not tied down to a particular airline for redemption

bmi Amex:
+ 1.5 Diamond Club miles for each £
- Points are tied to Diamond Club (i.e. Avios soon) - hence flight redemption options are limited

Based on this, I am thinking of using PRG card for travel/supermarkets etc where it is double points; and bmi Amex for other expenses - if just looking at accumulating the maximum points. However Amex MR does provide a lot more flexibility...

Or is the flexibility of MR + having all points in a single place a better option?

Anything else you can think of?

... I am thinking of using PRG card for travel/supermarkets etc where it is double points; and bmi Amex for other expenses - if just looking at accumulating the maximum points. However Amex MR does provide a lot more flexibility...

Or is the flexibility of MR + having all points in a single place a better option?
It depends on how much you value Avios.

I think I'd do exactly as you suggest - max out the MRs on travel and supermarkets with the PRG and use the BMI card for everything else indirectly earning Avios. And if you want Avios, you would still effectively earn 2 Avios per £ with your PRG spend on travel and supermarkets.

Given BA's relationship with AmEx, I wouldn't see the BMI AmEx lasting much longer.