It's easier by far to build a defender who is very striker heavy. Almost all of the defenders builds have a striker secondary and most feel the roll fairly well. Both Fighters and Wardens have builds that can make them very capable strikers without sacrificing much in the way of defending. It's always going to be easier to add damage to a defender build than add marking/defense to a striker. If you have to go striker, beast rangers do a decent job of sucking up the damage and controlling enemy positioning.