That snag jump is just not worth it for recovering, IMO. Watching Guy drop stocks because of it's distance really turns me off to it. I quite like the Duck Jump though, especially against characters that are fast. Being able to stall before flying up makes recoveries harder to cover, especialy if you mix in a wall jump before hand, keep them guessing. Although Snag is less predictable, you don't really have the freedom to play near the bottom of the blast zone like you do with the others. Maybe with certain MU's would I consider snag, like against a Mario who loves to Fair.
If you have your mind set on snag, you'll pretty much have to use platforms to prevent punishes on the end of the move, similar to default recovery.
It really depends on the matchup, but you're right, I really wish I submitted a 3113 set and I really regret underestimating default recovery.
The fact you can make zigzag go so high but stay in a general area makes it cover for default much better.
Snag helps a lot against characters who edgeguard via spikes/projectiles reliably (falcon, villager, megaman, etc), due to the speedy ascent. But this makes it more susceptible when the optimal option is to recover low (sheik, pikachu, dk, etc)
It also helps me edgeguard myself. I've started sh nairing from the ledge, then snagging back up to try and catch people recovering low. If I don't get the stage spike, I try to ledge drop dair. Not 100% sure if it's a true combo, but it is such a odd situation for them that it's likely to work, and if it doesn't, you're not likely to get punished.
In the case of pikachu and sheik though, it isn't a huge deal since the 3111 set is ideal in those matchups anyway.
Snag also helps DHD break out of certain combos/frame traps (jab locks, empty hop grab crap, jab mix-ups, etc)
Ex. I lost pretty decidedly to kenny the custom xanadu being uploaded today (despite it being 2:1, he SD'd) because I used 3123.
The gunmen did nothing, and my recovery cost me stocks and damage.
(I did the same this week vs Logic. Leave it to me to be the one to discover mega gunmen can't shoot pikachu and olimar reliably and thus are bad choices against them, but not actually utilize that knowledge in tournament)
The next custom tournament, I 2:0 Kenny and 2stock him game 2 with 3111. Default gunmen can actually shoot pikachu and default recovery lets me be trickier.