In my testing so far, Dragonite seems to work better in Dialgachomp, while Ambipom works better in Luxchomp and Sablelock. In Dialga builds with Energy Exchanger, you have multiple ways of grabbing your Warp Energy and DCEs, allowing you to spam Mach Blow more quickly. The main disadvantage to Ambipom is that, under some circumstances, smart players can play around him by Bronzonging extra energy to Garchomp, leaving him with one post-snipe. Also, if the Garchomp is spamming Earthquake for some reason, there is not much a 'pom can do. In builds that cannot get that crucial DCE consistently, however, Ambipom's speed would be preferred, since you would have a much more difficult time setting Dragonite up. It all just boils down to your list.