I would argue strongly that you learn Classical before Koine since Koine is basically a subset of Classical. While it sounds logical to start with smaller units and work up to the larger, it is in practice MUCH easier to learn more complex grammar first so that you'll be more comfortable with it over a longer period of time. Having learnt Attic first, reading the New Testament makes me feel over-confident in my Greek much like reading medieval Latin does to my Classical Latin. My guess is that if you learn Koine first, unless you set yourself learning Classical Greek with unusual punctiliousness, Classical Greek will remain mystifying and slightly outside your reach. But then again, this may be a state of affairs that's perfectly acceptable if you're honest with yourself about how much Attic Greek you plan to read.<br /><br />As for preferring Homeric Greek to Attic for learning first, Clyde Pharr makes a great case for the former in his textbook on Homer. I'd be slightly skeptical for two reasons: it's impossible to hear poetry without hearing prose and instinctively knowing how the two differ (I read Virgil before Cicero and it took years of exposure to prose for me to go back to Virgil with real appreciation); since my first suggestion is that you should learn first what you plan to spend the most time with, unless you fall in love with Homer, it's likely you'll be spending more time with Attic Greek so you ought to learn it first.<br /><br />Keep in mind that all of this advice is crap: ideal plans for a real world. Learn what grabs you and you'll keep doing it automatically. If you learn Koine first and then discover a deep love of Attic Greek it will barely matter that you had Koine initially, since your love of the language will motivate you to learn Attoc as well, if not better, than others who have learnt it with no particular attachment.<br /><br />In summary: it's a good decision to think about if you have definite goals about what you plan to accomplish, but if you don't really know what you want to devote yourself to (or are constrained by university courses, etc.), don't take the decision too seriously and enjoy the ride.<br /><br />Best wishes!<br />Adam<br /><br />PS<br />If it is university courses that are forcing you to learn Koine rather than Attic, by all means you should get in contact with your professor and let him know this. It's more than likely that he'll be able to give you extra material.