oil choices

[HeeTSynC]

Simple question, im gonna be servicing my falcon soon and at the moment have fully synthetic Nulon in it. The question is, should I put more nulon in it or go with penrite? I don't know much about oil but ive heard a bunch of guys on these forums swear by penrite. Also, is that Castrol "magnitech" or what ever its called any good? It seems a bit gimmiky but im not sure lol. Anyone used it?