Assuming by “regular angiography” you mean catheter angiography:

CT angiography (CTA) is usually better for initial diagnosis because it is fast, non-surgical, and uses an IV contrast injection rather than inserting a catheter into an artery. It is commonly used to look for narrowed or blocked vessels, aneurysms, pulmonary embolism, trauma-related vessel injury, and many coronary artery problems.

Catheter angiography is better when treatment may be needed at the same time. It provides very detailed images and allows the specialist to perform angioplasty, insert a stent, stop bleeding by embolization, or treat certain aneurysms during the same procedure.

So there is no single “better” test. CTA is often the first choice to diagnose. Catheter angiography is preferred if the result is uncertain, the anatomy is complex, or a procedure is likely needed. Both need caution in significant kidney impairment or prior iodinated contrast allergy. The RadiologyInfo CTA overview describes its speed and lower invasiveness, while catheter angiography guidance notes its superior procedural detail and ability to diagnose and treat in one session.

Which body part or condition is this for, such as heart arteries, brain vessels, legs, lungs, or kidney arteries?