It's pretty uncommon (not at all impossible, of course) to have enough ambient magnetic fields to worry about, and Hall effect sensors are good to whatever it says on the tin -- typical 5% or so, with 1% or a bit better being available, and beyond that you really should be considering a different technology as the baseline noise is just not very helpful when you're dealing with that much sensitivity. (That is to say, the dynamic range is about 40dB.)
For greater accuracy, VAC's line of saturating-ribbon servo sensors comes to mind?
Meanwhile, the bandwidth is not very good, if you need much more than 10s of kHz (Hall sensors go up to a few 100kHz, don't think I've seen more than that) you should really consider a shunt resistor, or current transformer if it's pulsating.
Note that, in a switching converter, while you can't put a CT on the inductor itself (in CCM), you can put a CT each on the two switching devices (diode/transistor), with a half-wave burden as well (diode into resistor). With a shared burden resistor, the sensed current will be continuous, while the current through each transformer is discontinuous (at least up or down to a modest duty cycle -- it fails when there isn't enough time to reset between pulses, so duty should stay in the 10-90% range, say).
Also also, if this is slow switching and 100% duty, consider a gate drive with charge pump power, or even a photovoltaic driver. Doesn't solve the current sense, but can handle one of two annoyances with high side N-ch application.
Tim