The size of ceramic tiles that have the best effect in an exhibition hall can depend on various factors, including the overall design aesthetic, the size of the space, and the preferences of the target audience. However, there are some general considerations that can guide the selection of tile sizes for an exhibition hall:

1. **Large Format Tiles:**
   - **Effect:** Large format tiles, typically those with dimensions of 24 inches by 24 inches or larger, can create a contemporary and luxurious effect. They are often favored for their seamless appearance and ability to make spaces look larger.

2. **Standard Sizes (12x12, 18x18):**
   - **Effect:** Standard-sized tiles, such as 12 inches by 12 inches or 18 inches by 18 inches, are versatile and widely used. They are suitable for various design styles and can be arranged in different patterns to create visual interest.

3. **Rectangular Tiles:**
   - **Effect:** Rectangular tiles, especially those in the plank-style or subway tile format, can add a sense of elongation to walls or floors. They are popular for creating modern and visually appealing patterns.

4. **Mosaic Tiles:**
   - **Effect:** Mosaic tiles, which come in small pieces mounted on a mesh or sheet, can be used to create intricate patterns or detailed designs. They are versatile and can be applied to both walls and floors.

5. **Hexagonal or Geometric Tiles:**
   - **Effect:** Hexagonal or geometric-shaped tiles add a unique and contemporary touch to the exhibition hall. These shapes can be arranged in interesting patterns to create a visually striking effect.

6. **Mix of Sizes:**
   - **Effect:** Combining different tile sizes within the exhibition space can create a dynamic and visually interesting effect. For example, a mix of large-format tiles with smaller accent tiles can add texture and variety.

7. **Porcelain Slabs:**
   - **Effect:** Porcelain slabs, which come in larger sizes like 24 inches by 48 inches or even larger, can provide a sleek and sophisticated appearance. They are suitable for creating seamless surfaces.

8. **Custom Patterns:**
   - **Effect:** Creating custom patterns with tiles of various sizes can make a bold design statement. This approach is often used to add artistic flair to the exhibition space.

9. **Symmetry and Proportion:**
   - **Effect:** Consider the overall symmetry and proportion of the exhibition hall. Large tiles in spacious areas can enhance a sense of openness, while smaller tiles may work well in more confined spaces.

10. **Light Reflectivity:**
    - **Effect:** The size of tiles can influence the way light is reflected in the space. Larger tiles with a polished finish may enhance light reflectivity, adding brightness to the exhibition hall.

When choosing the size of ceramic tiles for an exhibition hall, it's crucial to consider the design goals, the intended ambiance, and how the tiles will complement the overall theme of the exhibition. Additionally, seeking input from a professional designer or architect can provide valuable insights tailored to the specific context of the exhibition space.