The rapala knot is a very tight knot and as such can alter the action of any plug that doesn't have a split ring on it depending on whether it's dead center on the eyelet, towards the top or towards the bottom.
Even with a spit ring observe the position of the "split" in relation to the plug eyelet.
I prefer to use a snap swivel because currents can cause the plug to do some strange things, especially rotate & twist your line pretty bad.
Tom B.
(LongLine)