Nearly all folding bikes use aluminum rims, hence different manufacturing materials will not be discussed. There are three attributes that makes wheels "better", these are double wall, machined sidewalls, and spoke patterns ( bladed & spoke count )

Double wall rims are much stronger than single wall, hence these are ideal for folding bikes. Additionally it is less likely to get a pinch flat on the inside of the rim with a double wall. 

Machined sidewalls are essential to improve braking, they provide a rough surface for the brakes to create frictional forces. Slick rims are a big no-no nowadays.

Spoke patterns can lighten a bike, and create aerodynamic efficiency. Bladed spokes are the top of the line, while low spoke count paired spokes are also a good light alternative.