I am trying to decide if I should have flexible ducts or standard duct work(Metal) for AC being installed. What are the benefits and drawbacks of the two types of installation. I already have hot water heat.

Flexible ductwork is very restricing and costs way to much and doesn't work very well. My suggestion is use round pipe on all ductwork if you can, this will make the airflow smother to make transitions with take-offs etc.

I Just installed a central heating and cooling duct system im my 1300sq' home myself and the cost of flex ducting in realation to metal was about 1/10th. In addition the flex ducting comes already insulated to an R4. The prices I paid from Home Depot (California) are as follows
1. 8" X 25'-19.68
2. 10" X 25'- 21.93
3. 14" X 25'- 40.00
4. 16" x 25'- 50.00
Besides unless you live next to a fabricator what happens when something doesnt quite fit? I did the entire job 8 rooms in a weekend.
Good Luck

You must have missed my point. Flex is Crap don't use it period.