For instance, on a true 3 shotter vs. a reachable, should the tee shot be wider or narrower?
Generally speaking, I prefer wider fairways with a preffered side which is guarded by a hazard. Thus, one who successfully challenges the hazard will have a better chance of reaching the green in two or laying up safely.
Should bunkering force vertical (i.e. distance decisions) or accuracy (lateral decisions?)
Diagonal hazards that force both (i.e. farther left = farther to carry trouble)
Greens smaller, larger?
Large enough to accept a well struck approach with a longer club. Around the green, short grass with green tilted towards that side, bunkers opposite to create varying degrees of penalty for riskier/safer errant shots.
More contoured or less?
Depends. I detest holes that funnel everyone's drives and/or approaches to the same spot. I enjoy holes that feature turbo boosts for well-placed drives.
More shape or ovals?
No ovals.
Some of my favorite par 5s: Sand Hills # 1 and 16, Ballyneal # 8, Tobacco Road # 4, MPCC-Shore # 10, Lakota Canyon # 5, Morgan Creek # 5, 12 and 15