I spend long time in picking lumber. What do you look for when selecting boards?
I literally buy pressure-treated wood sight-unseen.

I live near a chain of lumber yards that offers convenient delivery at a reasonable price.  They offer pressure-treated fence posts with a consistent quality level, which is appropriate for my uses of the lumber.  I can call them up, ask for a number of fence posts cut to a particular length, and arrange for delivery.  The men at the lumber yard choose the posts (presumably from the top of the relevant stack), cut the lumber to length, strap it together, and put it on their truck.  I receive it, verify that it looks okay, store it (with appropriate spacers between boards), and use it as I need it.  I treat the cut ends of pressure-treated wood, either shortly after receipt, or before installation.

What I mean by "looks okay":


straight lines
no visible bow
no visible warpage
knots are not large enough to compromise structural strength
minor "checking" (shallow cracks at ends of posts) is okay
no deep cracks (that would turn the wood grain into a giant splinter)
no bark in the lumber
consistent grain width
grain direction is consistent with the shape of the lumber