Best and cheapest pre-paid plan for the iPhone?

So I'm looking into getting an iPhone plan for two people. Cricket has there iPhone 4 going for $250 with the plan costing $55. Walmart is selling there iPhone for $450 with the plan costing $45, but you can also use a walmart credit card to pay the phone of month by month without interest. Then lastly there's virgin mobile offering there iPhone for $350 with there plan costing $55 a month with unlimited everything however I would probably go with there $35 plan with a cap of 300 calling and unlimited everything else. Out of all of these or your guys opinions which one would be best or the easiest way to go. I'd like to keep my two phone bills below $100 and I don't really mind paying a lot of cash for the phone itself.

Walmart's plan, which uses Straight Talk, uses AT&T towers, but there unlimited data is not really unlimited data, they don't allow streaming of music and video, like YouTube and Pandora, or allow you to tether your phone like a personal Wi-Fi hotspot. However, it will have a faster data network vs Virgin Mobile and probably has better coverage overall. That would be my first choice if you don't do the things I mentioned, or else they will either throttle your speed or even cut you off for using too much data.

Virgin would be my second choice because they don't throttle data, but their coverage and speeds are not as good as Straight Tlk, but as far as saving money does, you will save $10/month.