I use medium poles everywhere. I like no poles but people with correct length or too long poles, it kills any possible style they have. No poles makes grabs look really steezy though! I like riding no poles in pow only once in a while of there are no relatively flat parts I'm dealing with.
Poles half of the time in park- they help my balance and can save me when I'm going down. Grabs do look better without, so I like that too. Always use noraml length poles for powder and all-mountain. They do get in the way when riding switch though.