There are loads of choices and most will do the job.
Obviously a high speed (which means a big aperture lens) is essential, due to unavoidable camera movement / vibration etc. Again, any DSLR will deliver 1/3000 in any normal daylight/sunlight situation and this is enough to counter even a high level of camera movement -
this pin sharp shot was taken handheld at about 1/3000 I think.
I use a Pentax *DL which at the time (2005) was one of the few reasonably compact DSLRs, most of them are for some bizzare reason huge. Nikons are good of course but their customer service has gone well and truly down the pan in the last few years.
However, really good shots are hard to do, due to window reflections, distortions, and dirt. Simple tricks involve placing a dark rag on your lap so as to kill window reflections, perhaps holding the rag near the camera. The camera needs to be v. close to the window but not actually touch it otherwise high frequency vibration gets conducted to it.
To do this properly you need a specially converted aircraft and a gyro stabilised camera mount.