The best way to do a Spiti trip is to enter via Shimla and exit via Manali because Shimla side gives gradual altitude gain which is safer and helps in acclimatization, while Manali side is shorter but more rough and adventurous; road conditions are good till Kinnaur and then become patchy towards Spiti, and Manali side has tougher stretches but is more scenic especially near Kunzum Pass and Chandratal Lake, so overall this route is the safest and most balanced option.