I tend to choose my subjects mainly on the interest I have in a particular aircraft. Having said that I then, in the majority of cases, strive to choose and replicate the markings of a particular famous pilot; in the case of British Aircraft most often a "Canadian Connection". The rare exception occurs when I'm particularly struck by the finish on a particular aircraft, such as the von Sachsenburg DVII with the yellow and black diamond scheme and the MFJ Pfalz D.III with the yellow trim and crossed swords and shield marking. The DH.2 that I'm presently working on was chosen by aircraft, then designated for Hawker's markings, then changed to accommodate the PC10 and grey scheme that I far preferred on the nacelle, in other words all over the map!

I guess what I'm really saying is the aircraft itself is the big factor here.
Cheers,
Lance