The four-wheel trolley has its benefits and shortfalls, like any other design.
Depending on the brand/design/etc of your four-wheel trolley, it may roll "easily" across a smooth surface (think tile, hardwood, etc). However, you will have to exert force in pushing a four-wheel trolley across airports that utilize carpets in their common areas (think Singapore's Changi Int'l).
Not all four-wheel trollies are built the same. The design, and assemblies for the wheel components differ between manufacturers and performance differs between hard/soft luggage. Some companies components are easier to replace than others.
You will always have the option to "pull" your trolley, like the two-wheel counterparts. If you revert to your old habits, at least you have the option to exercise two or four wheels.
Best of luck on your purchase decisions!