Buck boost converter + LDO or 2 Buck boost converter
Certainly the second option is the more cost effective. An LDO does not require as much external component as a buck-boost converter. This soultion saves some money by reducing the PCB size and the componenet costs.

On the other hand an LDO won't be as efficient as a buck-boost converter, but it all depends on the current demand of the bluetooth chip. I suppose we are talking about max 30 - 40 mA peak consumption here. That will be \$ \text{1.7 V} \times \text{40 mA} = \text{68 mW} \$ wasted energy. And it is the peak, most of the time the bluetooth chip will draw much less. So I would definietly go with the second option.

In general the switching converters efficiency is worse at light loads than at high (though you could find one with light-load-efficiency feature) so an LDO could be even better here.