Choosing the right power regulator for Battery powered designs
Battery powered projects (particularly those with periodic events spaced quite a bit apart) usually benefit from using a linear regulator. 

Looking at your requirements (LiPo 4.2V to Vo + dropout voltage) a linear regulator will be (on average 3.7V battery, regulated output 3.0V) 81% efficient which is close to the SMPS solution anyway.

A switch-mode device uses a lot of power (relatively speaking) just to power itself up; it is overall more efficient where a relatively large load current is being used.

What you need to look at carefully is \$I_q\$ for the regulator; this is the amount of current it draws simply to power the internal circuitry.

The regulator with the lowest \$I_q\$ that can handle the input and output voltages and required current is usually the best, but temperature rise is something to be considered - the small devices cannot dissipate much heat (there simply is insufficient physical packaging to permit it).

As most modern microcontrollers and many interfaces will run quite happily at 3.0V or even 2.7V, you should consider using that as the regulated voltage. If you really want Vo = 3.3V for Vin 3.0V &lt;> 4.2V you would need a buck-boost or some such arrangement. I would stick with a simple LDO regulator and drop the regulated voltage.

Note that regulators designed for large load currents (not the usual case for battery operated projects) will typically have a relatively high \$I_q\$

The most astounding part I have ever seen for \$I_q\$ : TPS783xx

Compare that with a buck SMPS that has a relatively low \$I_q\$ (for an SMPS device).

There are other considerations, but the no-load power dissipation of the regulator needs to be kept to a minimum.

Incidentally, a Li+ / LiPo can be safely discharged (in my experience) to about 2.7V