One of the nice things you have in your favor right now is that the JR 12 channel is finally out in some stores. Just so you can make better comparisons.
Your at the point where your going to make an investment in a piece of equipment you need to know subconsciously. Using your Tx has to be like reaching into your camera bag for a lens without thinking where your hand is going.
So what I'm saying is go to the hobby shops or clubs in your area and try out the Tx's to see how you like the feel of them on your hand because they do feel different. There is not a tremendous difference in size, but it is a big enough difference that you feel the difference in reaching for the switches with your fingers. Ideally, your fingers not on the sticks should be able to have the reach so the ends of them can fit in-between the toggles, your ring-finger and pinky are supporting the Tx. That way you can flick a toggle without having to search for it.
Buy more then you think you need, because what your doing now will change as new things come to market or you expand your skills.
You can do what most of us have done and buy small and wind up spending more money and time getting more channels. So this will save you money and "experience time" if you just go more from the start.
The DX-7 will work for basics, but when you start trying to add a stabilizer it can be done, but it is too complicated in setting it up without having a extra channel and switches to dedicate to the stabilizer. Your not going to fully utilize a multi axis camera mount with them.
So immediately your in the 9 channel range and your choices are the JR9303 or the Futaba 9's(PCM) or 10C.(both PCM or 2.4gHz)
Again, if you ever move up to a fully multi-axis camera mount you'll wish you had more channels.
A 12 channel will work for AP perhaps easiest of all because of the extra channels. Your choices are the JR 12 channel or the Futaba 12Z or Futaba FGH. Both the Futaba's are available in PCM or 2.4gHz.
One thing that irks me is that the Futaba's have different programming between them. Each one designed at a different time in life to incorporate the thinking at birth. So when somebody talks about setting up a 12Z, it is not the same on the 12FG or the 10C. It's not a major problem, but it is a thinking problem if it is a new radio for you and your using info from the forum to help you get started. It is no big deal though. When you get used to thinking "Futaba" it works out easy enough.
I haven't tried the Jr 12 in use since I switched to Futaba so I can't comment on the programming consistency between the 9303 and 12.
There is the issue about using video downlink frequencies compatibility with the Tx and this is something you need to research to find out more about.
The 14 channel is great if you have the money for it or can really justify it. It really does more then you need, right now
, but it will do everything you need. (these are tax deductable justified expenses if your doing AP photography for a living.)
Two other things.
First being whatever radio you buy-get a hard shell radio case for it.
Second which I'll catch some noise about is try the Phoenix simulator to see how you like it as opposed to the G4. Both work, it's just another "personal preference"!
"Vini, Vidi, Velcro"