How to choose a mitre box or a mitre block
There is no such thing as the best mitre box - the question should be: Which is best for you? There are many things that can affect your decision such as:
How often you are going to use your mitre box, and therefore how much are you willing to spend?
Is the mitre box needed for a specific project such as replacing skirting boards or is it for general purpose use?
How big is the workpiece - will you need an adjustable mitre box, for example?
What type of material will you be cutting and how neat and accurate does the cut have to be?
When choosing a mitre block always look for a solid beechwood construction with precise and neat saw guide slots, especially if cost isn't the major deciding factor.
Mitre blocks have two advantages over mitre boxes in that they are typically cheaper and the biggest advantage is that they can take virtually any width of workpiece as the workpiece is not constrained by the walls of a box.
As a rule of thumb, if you are going to be using the mitre box for one project alone it would be advisable to choose a mitre box specifically designed for that project, e.g. if you are tiling a bathroom and need to cut metal tile edging, a tiler's mitre box would be the preferred option.
Because the tiler's mitre box is designed to be used by tilers on a daily basis, it will not wear and become inaccurate whilst working on your project.
Some mitre boxes are made from either plastic or aluminium and generally speaking the aluminium version will last longer and maintain its accuracy longer.
If you intend to use a mini mitre box for a number of projects, an aluminium version would probably be a better long term buy, but if it is only for use in a small project the cheaper plastic variety may well be more suited to your needs.
When a mitre box is required to cut mitres for a variety of materials and sizes, a general purpose plastic mitre box would undoubtedly be the most practical solution.
When deciding which mitre box to buy, you need to consider how often you will use it, the size of the workpiece and the material you will be cutting.
If you intend to cut metal, you will be well advised to use a metal-sided mitre box as the saw guides are more resilient, but if you intend only to cut wood or plastics you can use a wooden or plastic mitre box as the guide slots will not be subjected to excessive wear.