[Adam43]

Crickey, that's a big one.

It basically comes down to what you want and how much you want to spend.

Do you want the roadster or the Coupe. I prefer the lines of the coupe, but you may like top down motoring.

Which series do you want?
I: has the better lines
II: Open headlights, but improved cooling and most importantly slightly better brakes. Probably the cheapest.
III: Has the V12 engine, which is a great engine, but then so is the 6cyl XK engine. More power, but much more weight. Slower. Has lost some of the lines IMO.

There is also the 2+2 option. Might be good if you have very small children.

For track days I would suggest I or II. III is much more of a Grand Tourer. Although all are good for this. Every year my Dad (who's car it is) and I go down to Le Mans, easily. Air con, perhaps, wouldn't go a miss, but that's about it.

Other than that the usual things about buying an old car apply. Get it checked out. The engines are good in both and should run for ages, but I guess the XK is easier to work on.