The architecture of both the Romans and Greeks are together called "Classical architecture." They have many characteristics in common for both of their structural designs. Their sense of symmetry and balance are connected with similar levels.
Here is how they differ in their architecture. The Greeks prefered marble and used it extensively for their construction projects. But the Romans invented concrete and used this material in most of their architectural designs. Various other differences are apparent, but it is quite difficult to assess if the Romans were better architects and builders than the Greeks.
It will be hard to say if it would be the Romans or the Greeks that can be considered as better architects. They both worked hard on the architecture that they created. The Greeks can be considered innovative because they started the columns. The Romans borrowed this concept and made everything more dramatic. It would be your own personal preference which type of decorative elements you would prefer.
A lot of minimalists would probably consider the Greeks to be better because while the designs are simple, they are also well-made. The Romans may have borrowed some of the concepts but it cannot be denied that they were able to do things that others were not able to do and achieve at that time.
Determining whether which group was better at architecture, the Greeks or the Romans, is a personal opinion. However, each has its own style. The Romans like arches and the Greeks like columns. There were three main column styles including Doric, Ionic and Corinthian. The Greeks liked the Corinthian style too.
The Greek architecture actually began first and then the Romans took ideas from the Greeks and then created their own architecture. Romans also created basilicas and temples. They wanted areas for people to come together.
The Greeks were probably better architects because they created stately columns that are easily recognized especially at the Greek structures that still exist in Greece today. Rome has structures too, but they are not as easily recognizable as Greek structures.