It's completely up to the company and/or captain. Some company use improved climb with bleeds off and on, some use it only with bleeds off, so in the end you may have 4 choices.
If you are not too heavy, so you can still use normal climb + bleeds off, you might consider using improved climb + bleeds off with assumed temperature. (There are companies who forbid this, most sensible ones don't though.)
I agree with John, using improved climb on short runways (especially when wet) when not neccessary isn't really very smart thing to do.
Note: Using improved climb will practically eliminate possibility of tailstrike on -400.