I think I'd get the M3L Brompton, myself, provided it was my daily driver. Best balance of weight and features to price (and perhaps, resale value, as it's most traditionally spec'd), but then I live in South Florida and there are no hills, so a 6 speed is generally unnecessary. I think doubling the budget from $600 to about $1400 is fair if you're riding daily and it's replacing the costs of a car or mass transit... but quadrupling the budget to $2200+ for a titanium model... for me that's getting harder to justify- that's approaching the annual cost to run my Honda Fit...