When the pre-order floodgates opened today for the iPad, in rushed waves of pundits ready to tell you which iPad you should purchase. We’re not going to offer advice of that sort for one major reason—we’re not quite sure yet that we should be advising any reader to go out and buy an iPad right away. This is, after all, the first-generation version of a major new product line for Apple, fraught with all the sort of question marks…