Generally speaking a PCMCIA and an internal wireless adapter will be equivalent.
Still speaking in general there are two aspects that make the internal adapter better. First and most important, the antenna for the PCMCIA card is contained in the approx. 1" by 2" "handle" that sticks out; the antenna for an internal card usually runs up both sides, or all around, the lid. Secondly, when moving the laptop you needn't even think about the internal pieces, but the PCMCIA card should be removed and put in its own little protector.