The bitcoin protocol is somewhat at odds with the desired goal of distributed mining. Only 1 entity gets the reward of mining a block, and only 144 blocks are mined per day. You are encouraged to join the strongest pools to have the highest chance of making money. According to blockchain.info, the top 6 mining pools control 75% of the market.
Statistically the reward is the same whether you're solo mining or in a pool. Actually less in a pool because they take a cut of the profits. The benefit of being in a pool is that you get the (smaller, since they're shared) rewards more frequently instead of waiting possibly years until you solo mine a block.
But there's really no reason why you have to be in the biggest pool, if you're in a pool with a 1/144 share of the hashrate you'll already be getting daily income, why do you need it to be more frequent?
Note: I think solo miners also get a bit more average latency when receiving bloks, I'm not sure if that offsets the cut the pools take enough to make the expected value of being in a pool higher or not.
https://blockchain.info/pools