Which one is faster: bigger or tileable texture?

Well, it's important to remember that memory and performance are often linked. Every time you make a call to the GPU to render something, you have to send along the appropriate data as well (textures, meshes, etc). Transfer time is one of the largest bottlenecks in rendering, so generally the less data you have to send, the better the performance.

Thus, to answer your question, tiling is probably better for performance.