Consider the after sales service!
As with buy most things it is important to consider the after care that a company provides for their products, albeit in the hope that you'll never need to use it!
Sticking with the major brands is a great way to ensure that you'll be well looked after in the unlikely event that something does go wrong with your unit.
It is worth noting that most warranties are UK based with the exception of Suunto who offer a worldwide warranty scheme alongside an extended UK warranty.
Read more about Suunto's Warranty Policy here.