Thank you for the response,
By "powerful" I simply mean exerts a greater influence. To be more precise, atomic radius increases from right to left and from top to bottom, so which element would be larger, one located in the top left or one located at the bottom right? Both elements would satisfy only part of the trend to be considered "large", so of the two which is larger, and why? I have found questions like this, and have been unsure which aspect of this trend has a greater influence on atomic radius.
Moreover, the question can also be expanded to included such trends as electronegativity, ionization energy, metallic character, etc. For example, EN increases from left to right and from bottom to top, so would At (bottom right) be stronger than Li (top left).
To sum up, I am simply curious which aspect of the periodic trends is having a greater influence (horizontal or vertical) for any of the trends.