The Slant Style became popular in the 90's because it can be stamped and textured or done in regular gray concrete as can the mower style. But, unlike the mower style, it has the unique ability to also hold in gardening materials because the back of the curb is higher than the front.
The front side of the curb is generally set at ground level to accommodate lawn mower wheels. The slanted look shows off any texturing or stamping that may be applied.
The Mower Style is very popular because it is installed to both accommodate a lawn mower wheel and at the same time retain gardening materials because of its higher back side. It also has great curb appeal because it sets off the landscaping with a picture frame type of look.