I vote keg first then AG - assuming your kit beers are palatable.
Less for the reasons that other people have mentioned (lack of bottle cleaning and care, cool factor etc) than for beer quality reasons.
I think that by going with a keg system, you will be able to more easily get teh carbonation right for the style of beer you are brewing, and correct carbonation is massively important for beer flavour. I also think that in most circumstances, beer tastes and looks better if it is clear and free of suspended yeast. This is a hell of a lot easier to achieve in a keg than in bottles.
Bottle conditioning seems to be a bit of an arcane skill, and most of the times I have tasted bottle conditioned homebrew - the carbonation isn't right. The beers might have been really nice, but they would have been better with the right carbonation.
I went AG before I went keg.. but in retrospect, I think that I could have gotten a greater quality difference in my beer with kegs than I did with AG.
Like I said though - thats all only if you are happy with the quality of your kit beers/partials/extract brews
TB