Win_arc -- hard to say as only you know your space and $ limits. There is not nearly as much to choose from yet in 1:200 so you will be very limited if you focus on that scale, no Su-34s yet, for example
I would never recommend sticking hard to one scale -- though many do -- as I just feel that limits you. You might want to consider 1:200 for jets you like and 1:72 for jets that you really, really like and are only availlable in 1:72??
And don't think that 1:200 is necessarily cheaper -- many have MSRPs that are right up there with 1:72 prices if not more
But that series of 1:200 Flankers that is out now is simply really, really... really
Pic one up and see for yourself first hand and go from there (don't sell those new gaincorps yet!).