So wait, maybe I'm not getting this quite right. Is the amount of Bitcoins you receive from the block directly proportional to your speed?
Yeah, like sirky said, that's pretty much it. So let's say for example you are in a pool that is pushing 50 GH/sec total and you are putting in 1 GH/sec towards that. When you're pool finds a block of 50 coins you'd get a percentage of what you put in, which in this case is 1/50th and you'd get 1 of the coins.
You'll see a huge variance of pools and none of them are really better. Deepbit is at 2200 GH/sec right now, so if you were mining for them with your 1 GH/sec, you'd get 1/2200th of a coin or .02 coins every time the pool found a block, but with 2200 GH/sec, deepbit is going to find blocks a lot more often than smaller pools.
So in the end, it works out pretty much evenly no matter what pool you pick. You either get larger rewards less frequently, or smaller rewards more frequently. Just look at what the pools offer and make your choice based on their fees, offerings, etc, and don't get too worried over the rewards.