pools allow for further decentralization of bitcoin mining by allowing small miners to continue to mine at such a high difficulty.
It is not that you have any choice now to be a solo miner. Solo mining requires a lot of hashpower and is not for the easy to setup.
1. While in pool mining you will get paid everyday, in solo there is no guarantee that you will earn anything if you are unlucky.
2. Pool mining requires almost no knowledge about mining setup you leave most of the headaches to the pool admin.
Solo mining is only possible if you have tremendous hardware and are technically skilled enough to setup your own pool it is not really choice anymore, it is necessity.