Какой css код более правильный?

<div  class="just-block">
     <h2>Hello world</h2>
</div>

<div class="navigation">
     <h2>Site Nav </h2>
</div>

.just-block {
width: 100px;
height: 100px;
background: #fff;
}

.just-block h2 {
font-size: 24px;
color: #777;
}

.navigation {
width: 500px;
height: 300px;
background: #eee;
}

.navigation h2 {
font-size: 17px;
color: #ccc;
}

<div  class="just-block">
     <h2 class="font-size-large">Hello world</h2>
</div>

<div  class="navigation">
     <h2 class="font-size-medium">Hello world</h2>
</div>

.just-block {
width: 100px;
height: 100px;
background: #fff;
}

.navigation {
width: 100px;
height: 100px;
background: #fff;
}

.font-size-large {
font-size: 32px;
}

.font-size-medium {
font-size: 22px;
}