Picking the right scale for your model trains is an important decision, as it will affect the size, cost, and available selection of trains and accessories. Here are a few factors to consider when selecting a scale:

1. Space: The scale you choose will be influenced by the amount of space you have available for your layout. Smaller scales, such as N or HO, are more suitable for smaller spaces, while larger scales, such as O or G, will require more room.
2. Detail: The scale of your model trains will also affect the level of detail you can achieve. Smaller scales, such as HO, offer a high level of detail, while larger scales, such as O or G, may be less detailed but may be easier to work with.
3. Cost: The scale of your model trains will also affect the cost of the trains and accessories. Larger scales, such as O or G, tend to be more expensive, while smaller scales, such as N or HO, are generally more affordable.
4. Selection: Different scales have different levels of popularity, which will affect the selection of trains and accessories that are available. Some scales, such as N or HO, have a large selection of trains and accessories, while others, such as O or G, may have a more limited selection.

Ultimately, the scale you choose will depend on your personal preferences and the space and budget you have available. It may be helpful to visit a hobby shop or club to see different scales in person, or to research online to get a better understanding of the pros and cons of each scale.