Only been to each place once but I would say Phuket is by far better than Bali.
In my opinion (albeit the two trips) Phuket is more developed than Bali.
The food is better in Phuket and the shopping is better too and much better quality clothing.
I love the Thai's and got very emotional when I left. The Balinese are great too but I found the hospitality better in Phuket.
Bali is great, don't be me wrong but I would pick Phuket every time.