red top or black top

Hello I am looking to buy with a skline motor a sr20det I believe is the most popular one but I keep seeing these ads that sa the motor that they put in the car is a red top or black top is one better that the other? I have no clue and also what should I look for in telling if the swap is a good one? An information would be of great help thank you

Redtop is the older model which came in the 89-93 S13's if I recall and the blacktop is the ones from 94-98 or.

Basically the Redtop motor is older and if you get one might have more miles on it, the blacktop is newer so less miles on that motor.