Is it better to have different archetype abilities or focus on 1 archetype?

As the title, for a general guide for each class, is it better to focus on 1 tree or 2?

As the tree goes down, the abilities become more powerful (I suppose). However, some other abilities from another archetype makes the abilities more powerful.

Here are some examples.
Many mage players play rift-bender. Although the light bender seems to do the most damage among all (I'm not too sure), the "winded" ability of riftwalker lets the enemies take more damage.
Some shaman players play full arcolyte, which (maybe) does the highest dps. Some mixes the ability tree with ritualist's "mask" abilities for some reason.
Just recently I saw a video of an assassin guide which mixes shadestepper with trickster. Trickster clones provides more sustain and amplifies the damage; shadestepper abilities do lots of damage with "marked" ability.

What's your thoughts on mixing archetypes? Can I have advice for each class?