The single most important aspect of a helmet -- for both comfort and protection -- is its fit. If this one fits you perfectly, stick with it, and when you need a new one, give serious thought to buying another one just like it. (Unless you shop around and find an even better fit.)
One thing to keep in mind, though: if the helmet has taken any kind of hard impact, in a crash or just from being dropped, then replace it even if you see no visible damage. A helmet is good for one impact, then it's done its job and should be retired with honor.