Well, it depends on your hashrate.
To me, anything above 450h/s is good enough for solo mining, but you could gain more from pool mining.
Anything above 600h/s will be very good for solo mining, and would be better to help decentralisation.
Anything below 450h/s, I would recommend pool mining, as you can gain more from submitting shares.
So, mainly it comes down to your hashing power. It is better to do solo mining, as the reward is higher and you help decentralisation. On the other hand, if you want to gain reward quickly at a smaller amount, then pool mining is a better option