nabblbeast, if u use condensor head, than problems is more pronounced. the reason is that very quekly the negative is hot from the light sourse and it changes the form. so what u do is that u focus on the centere which is not on the same plane as other parts. anti-newton helps very much, but be aware of dust etc. u have to be even cleaner than befor.
align the enlarger of course. and yes, better lenses helps. but only when u have made the besic things -alighned enlarger and flat negative.
also, if u print with the filters, wether the normal head(deffused) or with the condensor or the cold (with filters), make sure to change filters very gently, and wait abit, couse the vibration makes problems.