for electric instruments, an in-line tuner will always track clearer and faster, as it's getting a much stronger input.
the polytune is good (especially in "stream" mode, where it's +/- .5 cents accurate). the strobostomp will be more accurate still at .1 cents, and the sonic research turbo-tuner will be the tightest of the bunch at .02 cents.
Guitar Repair Gnome
Alpha Music, VA Beach