International students aren't eligible for concession tickets, rightly or wrongly so (not getting into this debate). None the less it sucks for you.
Myki is slighly cheaper and you can register your card online, so, if you ever lose it, you can transfer your credit to another card. Whereas with the old metcard paper ticket, if you lost it, you are fucked. I dont like how they can track you using the myki though and that they keep that data but hey each to their own.
Personally i still use the metcard because one im politically opposed to the whole myki system and i was kind of hoping if enough people stuck on metcards they'd decide to scrap it, two i dont need to cause a massive pile up on the barriers and three it just seems like more hassle than its worth.
Take into account when and how often you'll be traveling as well. If its only once or twice a week a yearly might not be the most cost effective option. I know they sell 5 x daily and 10 x 2 hour tickets. So, that'll be great if you dont go to uni 5 days a week. You can kind of scam the 2 hour tickets as well, if you're close to the next hour, it counts it as being the next hour, so you get like...3 hours. If you use them after 6pm (i think) its valid until 3am the next day.