Archmages benefit from better burst healing than Pale Masters. Pale Masters can heal better in non-burst situations, where by "better" we mean "relying upon fewer expendable resources". In short, it's cheaper to heal yourself as a Pale Master, but not always as reliable. If you're not loaded with the cash needed to buy Reconstruct scrolls and Oils of Serious Repair, then Pale Master is a great option. If you can afford it, then the WF Archmage heals way better.

Archmages also get more spell points than Pale Masters, and for your first time on a wizzie, this is a good thing. And finally, an Archmage is easier probably a bit easier to gear. But in case you want to go Pale Master, make sure you hit up the Mabar event.

This is simply not the time to be worrying about how your necro DC's will look in Elite or Epic Lord of Blades, pace Mrmorphling. Play whatever you want now. You can always change your toon later. Switching between Archmage and Palemaster is a matter of changing enhancements and potentially swapping a feat. Provided you're Warforged, you can switch between them with no loss of healing whenever you like. If you're not Warforged, you really need to be a Pale Master.