When in doubt, go with whatever collectors value more (i.e. more expensive).
Ms. Marvel #18 appears to be it.
Side note: Sometimes for example, a character has a quick cameo but doesn't appear in full until the next issue. This happens with Wolverine in Incredible Hulk #180 and #181. He has a quick cameo on the last page of #180.... so some people assume that would be his "first appearance" but not so. Collectors speak with their dollars and Incredible Hulk #181 is the TRUE first appearance and that is worth way, way more than #180 (which still commands a nice price itself anyways).
