Just remember, lens is always more important than camera.....those cameras are all very expensive and are probably a bit overkill for a first SLR. I'd buy something like a new 550D (Very similar to a 7D but without a few features), or a second hand 40 or 50D, then spend the rest of the money on a decent long lens (the 18-200 is good considering the huge range, but IQ is always better the smaller the range of the zoom). The 70-300 IS lens (not the new L version) is very good, as is the 100-400 that I use. Ideally you'd want to get a 300 f4 prime if IQ is important (or even better, the f2.8)

However, if you are intent on getting one of those three cameras (which I think would probably be a bit of a waste of money considering the xxxD range is very capable), I'd go for the 7D (what I'm currently using). The 60D is just awful. A massive step backwards from the 50D and I don't know of anyone who's bought one. The 5Dii is more of a studio camera. It's full frame, which is good for many things, but not aircraft photography where reach is everything.

I learn't on a 400D....its a superb little camera and I used it for 3 years. For the first year I had a basic 75-300 lens. In total, my kit cost me £500 and could produce some decent shots. Then I upgraded the lens (a year later), as this is the most important part of the camera to the 100-400, before finally upgrading the camera to a 7D (3 years later)

.mic

Before anyone can give advice to you, a question has to be asked.......How much photographic experience do you have and how much are you willing to learn so you can apply that info into the capturing of images and not wasting your money on an expensive tool, or wasting your time getting more than you'll ever foresee a need for..........

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You should also consider what you want to do with your photos. Most modern compact cameras are capable of taking high quality photos & have far more features than most people will need for normal purposes.

I agree with Mic about the cameras you've listed. (Click on his sig to see examples of his work.) Also that the lens is more important than the camera.  I would add that the person behind the lens is most important of all.

After this past weekend shooting with some guys that use some serious bits of kit, I can honestly say, if you can afford it, buy it. However that also comes with the proviso that you are going to take it seriously. All the stuff about starting off with something basic is all well and good, but the reality is the higher end stuff will still do all the basic stuff, plus as your learning it'll allow you to expand without having to fork out more money on more equiptment. One of the guys this weekend was shooting with a 7D and a 5D, but he was carrying round two bag fulls of lenses, all of which got used, to him it wasn't so much about the camera but the lens he needed for the situation.
The other guy was working with a 40D I believe but his bags were full of flashes, home made filters, lenses and so on. And watching how he used them and the thought process behind it really opened my eyes to what the difference is between your sunday afternoon shooter and what you really can do if your willing to learn. If your willing to learn, take it seriously and advance go straight for a 7D and save your money for equiptment in the long haul. If your looking at it as more of a hobby for the occasional weekend, go with a lower end camera and use the money on lenses as you need them.
It's not just learning about the ISO's and the appertures, and such, to many people these days think because they know these things they are an expert, Take a look at some of Mic's shots, not nessicarily his aircraft shots, he's got a good sense of what makes a nice photo, the same can be said for Ken and Doug and Steve (61-otu).