Base in Sigiriya for all 3 days and do a food-first loop around the Cultural Triangle: local breakfast and rice-and-curry lunches, Sigiriya/Pidurangala for nature, then Polonnaruwa and a safari day. This works because it minimizes transfer time, keeps you in the one part of Sri Lanka where 3 days can still feel complete, and gives you the highest-value food and nature mix without burning the budget on long intercity travel.