For a bunch of cars 45+ years old each one should stand on it's own merits. There is no longer good, better, best model. The MK2's are the most desirable based on the 289" engine and their scarcity- only 700 +/- made. They are also selling for a premium for that reason.
As a person who just bought a basket case I shouldn't talk, but common sense dictates buying the best one you can afford. Some parts are extremely rare and more expensive than an MGB for instance
Common additions/ changes include all the "LAT" options, additional cooling aids , four barrel carb and manifold, fancy wheels, etc. As with any old crock, rust is not your friend. Adding to this is the possibility that any purported Tiger could be a clone or a recycled Alpine. Best to find a Tiger owner to walk him through the process. Bob