When it comes to model trains, it is not so much the case of one scale being 'better' than another but rather which is more appropriate to your needs.
Given that a HO train is half the size of an O train, many collectors recommend this size to those who are just starting out, as they won't take up as much space, and you will have more room for decorations and accessories.
In some cases, O train sets will be more expensive due to their larger size.
To find the perfect model train scale and set, do plenty of research online before making your purchase.