A great leap sideways
Irrespective of weight, unless you're hucking, or jumping stuff, and are really hard on crank spindles, the Middleburns are the better choice. This is a total "No Brainer" to me:
In relation to the "Mr Whirlys, the Middleburn's will offer a better chainline: all the outboard bearing design triples have dismal chain lines compared to square taper and Isis BB's. Important? Just wait for that first big, long, muddy ride......hello chain suck.
Then there's the weather sealing issue: the outboard BB's don't have a great track record @ this either. Add drag from the larger seals and this is only partially addressed with ceramic bearing on the outboard designs, in relation to the Sq. tapers/Isis BB's.
Now, the BB30 designs, etc.are trying to address the Q-factor issues of the outboards by modifying the existing BB dimensions, to solve a problem that doesn't really exist in great measure previously.
Basically, as much as I'd like all the latest iterations of BB/crank design, they're all a great leap sideways at best compared to the nearly completely forgotten Sq. tapers.
I could go on, but, I've got things to do. Short answer - get the Middleburns.