As as Engineer or a Guardian you will find that you are one of the two races with no speed boost skill built in. So you need to find a way to move faster. Runes are the answer.
There are two types of runes that boost your speed if you use all 6 of them. That is, if you use an identical rune in all your armor pieces.
Superior Rune of the Traveler and Superior Rune of Speed both provide a 25% boost in movement speed, but the Traveler Rune costs almost 3 times as much.