If they still have those 2 month free trials, try and get one of those. Because then you can try it for 2 months, and you can edit how you want to pay for xbox live. It lets you pay monthly or yearly. Monthly is around 7 bucks, and for a year it is around 50. But if you want a whole year now, then go with the 12 month card.
well a few things to consider 1. if you plan on modding your Xbox or have a modded Xbox make sure it will work with XBL before you go buying a card and getting instantly banned. 2. I would go with the smallest amount of time you can get. That way if you do not like it you have not wasted money 3. there are also free online gaming systems out there Xlink Kai and XBconnect depending on what game you want to play you can check them out and see if the games you like are on the free system. Xlink Kai has quite a few, and once you meet a few friends you can all get together and play. Playing in already open rooms is ok, but you will find a lot of people using cheats on those, so meeting people who do not cheat and then setting up your own private, password protected room so you can play without cheaters joining in and ruining your game is the best way to do it.