OP,at $1000 per Python,buy all three!You will easily sell them for more than that if you choose to
The classic Python remains the 6 inch blued and would be my first choice.The stainless does tend to command higher prices,especially in the "ultimate" finish(ie highly polished),itys very pretty,but tends to scratch quite easily.Ive never been really keen on pythons with 8 inch barrels,they just dont look right,but I still wouldnt turn one down.
There are many other factors that determine a pythons value,condition,age(generally the older the better,stainlessvs blue vs nickle etc)
Pythons are really fantastic guns and seem to be getting harder to come by,people hang on to them I guess,so if you have a chance to get one(or three!),go for it!