Model trains come in many different sizes, or scales. For those just getting started in the hobby, deciding on a scale for themselves or their children can be a big dilemma. The short answer is that there is no one single "best" scale of course, but there may be the best scale for you.
If you're trying to determine what scale model train you should buy, you need to know how many different options you have.
Read up on different scales and their proportions to the prototype. You should also learn the difference between scale and gauge. You can also get more details on a specific scale by following these links:
Making Your Decision
Now that you know a little more about your options, which scale is best for you? To answer that, let's find out a little more about you.
Age is often considered a factor when buying model trains for children, but the decision doesn't get any easier with age. Many modelers find the larger scales more comfortable as vision and dexterity strain in their senior years.
It's not the size of the trains but the size of the layout. Even an efficiency apartment has room for model railroading, it all depends on your goals. Bigger isn't always better. If you don't have room/desire for a large layout, there are still many options: a smaller scale to pack in the most scenery, a mid-size scale switching layout, larger scale modules or static displays.
We all work on a budget, some tighter than others. The relationship of scale and cost isn't quite as simple as you'd think. Cheap and expensive models are available in every size. One difference is how many models of a given size you'll need to fill your layout's space. In other words, do you buy a 20 car train of $20 HO scale cars or an 8 car train of $50 O scale cars? Both will cost you about the same amount in both your wallet and your platform.
Ultimately, it comes down to what you enjoy most about the hobby and what you want to do. Balancing these goals with your available space, budget, and physical abilities will yield the perfect compromise. Do you enjoy scratch building and detailing, or would you prefer ready-to-run models? Do you want a continuous run, lots of animated accessories, prototype-based operating plans, multi-person operating sessions, complicated switching challenges, big scenery, something portable, or a combination of any of the above?