I would say wait a couple of days until the Ambassador stats are released (people can start earning it in 2, so they have to release the stats soon). As things stand now, the Excelsior rules the roost of the Fed C-Store DPS cruisers. The high turn rate lets it use narrower arc weapons, and it still has solid engineering capability (the Regent falls a little short in that regard by having only 6 eng slots, which limits your ability to tank while supporting with heals or EWP).
Agree about the excelsior. With the right build she holds her own well, especially as an all cannon build.... fun! If you can get the Fleet version if cruisers are your thing. Otherwise the c-store versions are fine, especially the refit.
As for the Ambassador, seems to me it will be most likely a Galaxy variant so I wouldn't keep my hopes up about a great turn rate on that ship. Coming from mainly escorts, you may find the turn rate of any ship bar the excelsior (and perhaps sovvie) lack lustre.
"The world ain't all sunshine and rainbows. It's a very mean and nasty place and I don't care how tough you are it will beat you to your knees and keep you there permanently if you let it. You, me, or nobody is gonna hit as hard as life. But it ain't about how hard ya hit. It's about how hard you can get hit and keep moving forward." - Rocky Balboa (2006)