Depending on your budget not to include the camera, the F550 would be a good choice. I find the Phantoms ability to control and hover a little smoother then my F450. I am still dialing in the gains but I don't see it getting much better. I have everything to turn it into an F550 except the 2 extra motors at this poing. I added the extra arms, ESC's and plates so I can compare a 550 to a 450.
I purchased the Phantom and am having a lot of fun with it but I do see the limits of not having a full gimbal. I want to do so much more but am struggling with both flying it and getting smooth video. I am sure with time both will get better. I hope you post up the results of the conversion from 450 to 550. From video I have seen it looks like the 6 rotor 550 is a more stable platform to start with and carries a gimble with ease.