Phoenix is better at output stabilized hashrate.
I like cgminer's "total control" aspect, but it seems that its outputs are not as stable as phoenix. Sometimes my gpu activities are lower to 0% for, say 30 seconds. Also, the hashrate would swing between 15% and -15%.
My best approach for cgminer is to disable cgminer's ADL support (--no-adl) and control the gpu by MSI afterburner or other tools. However, its hashrates are still not so stabilized.
Now I use Phoenix 1.7.0. Its hashrate are very stable once it got configured (about 1% ~ -1%). I also use atitweak to fix the fan speed and gpu clock instead of dynamically tuning.
CGminer is great for it's total control aspect, but I do think phoenix miner got better hash rates for me, although, I had greater CPU usage which led to more crashes.
This is on 5970's BTW.
I'm sticking with cgminer for the ease of use. Also Ckolivas is pretty on the ball with his support.