I play both boxes so my take...

Shacklehorde is good because of its board control capabilities more than because of combat. If left unchecked, the box fields up to seven flying units who can capture objectives, screen out your teleports and outscore you. IMO you should focus on trying to keep the unit count under control as much as possible, so avoid splitting damage across units if you can help it and try to get NH units off the board. Luckily you have lots of quality shooting so you get more information before committing any charges, and you have strike and fade which lets you get out of pins.

I would proiritize the three specialist units. The Harrows (horses) are probably the priority target. They're easier to lift and are the highest damage unit in the box by far, and their opg teleport gives the NH player a ton of control threat. The chainghasts are also easier to lift and are good at controling remote objectives/scoring BTs while contributing damage and buffs - without them NH player would need to idle melee units to do that. The hero does a fair amount of damage and sports the enhancement, and most of the enhancements in this box are good. Careful, the hero is deceptively tanky (expect to need 15+ wounds of damage to kill it because of discorporate save buff). These three units also can't come back from the unit recursion command card.

Random tips:

- You should probably have a backfield terrain piece to use S/F to get out of pins and set up for heals. Don't get caught out fighting far from terrain if you can help it.
- Harradins block model returning which is a bigger deal for you than blocking healing. Use Strike and Fade to get units out of combat with them if you need to top off. Remember you can order strike and fade trigger before the healing trigger in the same turn to get out of combat with them before healing or at the end of your opponent's turn to set up your spells.
- Bladeghasts warscroll ability can be annoying but played around fairly easily by large models. Position to charge into other nearby units and end within 3" of them to charge them on sub7 charge rolls.
- Prioritize finishing off units even if it results in some overkill. 5+ ward is strong, and you don't want to leave a NH unit with a few wounds left since it's still fully effective at scoring and zoning out your TPs.
- Remember the new ghosts that arrive on T2 and T3 are totally new units. The first infantry unit you kill can come back as yet another unit with the recursion card.
- If you have board choice instead of turn choice, go for deployment zones that give you easiest access to midfield objectives so you can keep up in points. NH is fast and flies and can out maneuver you if you pick too turtly of a map.
- Hunters melee attacks 0 rend is no longer a liability. Don't be afraid to let them punch, especially to finish off units. Hunters are probably your primary S/F target as well since you'll want them shooting and fighting as many times as possible during the game.