Garlic Powder vs Garlic
Both may be preferable as they provide different garlic flavours. 


Fresh garlic is sharp, and has bite. It tastes fresh, and works especially well with other bold flavours and fresh ingredients.
Granulated (roasted) garlic is garlicy, but nowhere near as sharp. It tastes more like the prepared garlic flavour we've all become accustomed to. It's a mellower, deeper flavour.
Roasted fresh garlic is garlicy, mellow, and deeper than either granulated or fresh garlic. It's brilliant in smooth things like soup or mashed potatoes, and is also a much deeper flavour on a pizza with other roasted things.


One of the coolest things about these different forms of garlic is that you can use them together to pack more punch. Not only can you combine them, but you can add them at different times in a preparation to layer the goodness in interesting ways.

"Preferable" is all about taste, your (and your guests') preferences, and depth.

When I make pizza, for example, I use both marinated garlic and chopped fresh garlic. Sometimes I'll even add roasted garlic over the sauce, especially if the pizza has sun dried tomatoes.