That is true of luck but there other important factors when choosing a pool. The payout systems and fees are what will make the real difference to the returns you receive for mining. Unlike Bitminter some pools only share out the block reward and do not pay the tx fees they collect. That's a large proportion of the income these days. With only a 1% fee you'll find Bitminter is one of the best. Also, you should look back through this thread to see how helpful and knowledgeable DrHaribo is. He always puts in the time and effort to help his customers out (and he'll probably come along soon and answer this question much better than I just did).