Depends upon what you'll be doing with it, if it might have to change to a 2x10, etc.
This will make you decide which GRIPS you wish the solid to have, if that is of any importance.
The 'design intent' of that particular plank/board/stud will have to be taken into consideration. If you create a 2x12 (I know that's not the final dims) rectangle and extrude it, you will get a different set of grips after the object is extruded than if you used a region instead of a rectangle. Additionally still, you will have different options if you simply use -BOX- to create the solid. Mainly, a Box can be additionally extruded either direction along the Z axis, as long as having arrow grips along each face to allow you to increase the width/length of the box without having to move each pair of corresponding vertices. Rectangle-extrusions lack this.
If you want to go the other way and LOCK DOWN what post-modeling modifications can be made, a REGION extruded cannot change profile without using the SOLIDEDIT or PRESSPULL type of commands. The only caveat to that is that sometime, they apparently added an arrow grip to the destination face of the extruded region that allows you to dynamically adjust the TAPER of the extrusion. In case the guys at the saw mill had their blade crooked, in this case.
You can also SWEEP a rectangle along a path in case there's some warp in your timber, and add a bit of twist angle to it.
Then you run into special situations where you use a LOFT in either method; a two-profile (start and end sections) or a single profile and path. You could get into multiple profiles and combine them all with the path, but I think I've already complicated a hunk of timber enough. This could happen in case one of the corners is lopped or rotted off along the extruded edge.
See attached drawing for examples.
Since you said 'realistic' - should I get into applying materials to the object?
ETA: Sorry, just got out of a long 3D model review, and I'm a bit wired on Monster energy drinks because I had to get up at 4am for this meeting with some Aussies.