The faster gunmen is probably the worst imo. It's essentially just a less potent frisbee, the main boon of gunmen is the body they leave to absorb stuff for you and fast gunmen barely stays out. The range is really bad, like to the point you'd need to be within easy dash attack range for it to work. It's just a really obvious projectile you can't even do anything while it goes off. At least default waits a bit to apply pressure on the ground for you.
Duck hunt to me is one of the few characters who's default set is pretty much the best. The only arguable stuff is:
Zig Zag Can: Very radical special, probably amazing in doubles for all the disruption it can do but it isn't really better at pressure than the default and also doesn't have the proper trajectory to work with your other projectiles as well. It's also much harder to use for generally less payoff.
Mega Gunmen: Real helpful in the projectile wars. Absorbs tons of crap and threatens their position with a long, awkwardly timed shot. Though against lesser or no projectile chars, pretty useless. Can't lock the hitboxes down with hovering can as well as original gunmen though, and also doesn't work well to add more pressure when clan and frisbee are out as consistently.
I used to think I'd use it because I hated projectile wars, but the matchups aren't bad. And default gunmen helps with out bad/iffy matchups by shutting down ground approaches. (little mac, sheik, greninja)
Up Special:
Snag is good if you plan on planking a lot. The shorter distance doesn't hurt you that much unless you go really deep on edgeguarding with your body.
Super Duck Jump is just super safe. It goes higher, has invincibility frames, and a windpush for added safety/fun.
Both of these hinder your ability to go aggro though. The default doesn't go as high as super but with the horizontal movement it lets you come back from farther and from more dangerous situations. And snag is safeish and has some fun aggro stuff to do with how much duck hunt pops them up and has a way to protect his landing if a can is down there. Also has good horizontal movement and generally it goes far enough to let you recover unless you lost your double jump.
A lot of people worry about the default and it's lacking hitbox, but since it goes so far, you can just put out a hitbox of your own to accompany you. Via can or gunmen before you begin your ascent. Clay shot if you do it with your double jump from the right distance but it isn't very reliable still.
These aren't possible with the other up specials since you need to devote all your time to moving horizontally.