I wouldn't use the premade gangs. Much more fun to come up with your own ideas, especially if you're willing to do some basic conversions (weapon swaps and the like). I'd also recommend using weapon combinations that look cool/interesting rather than just going with what the internet considers the optimal cookie cutter builds (more fun for you and your opponent).
For the Goliaths I'd suggest starting with one each of the main weapons, 1 grenade launcher, 1 combat shotgun +
CC weapon, 1 plasma/stubber +
CC weapon, 1 renderiser and 2 or 3 stub cannons. Add in a stub gun and
CC weapon (can represent a Juve), the rivet cannon if you like the idea and do what you think looks cool for other model(s) (another grenade launcher or combat shotgun are fun options). The Goliaths are somewhat limited in their poses so you will need to be creative to prevent models looking like carbon copies of each other.
The Escher are harder as they've got a lot more variety and options than the Goliaths. The bolter/needler is a good weapon and the leader looks cool with the coat, The shock whip is also a decent weapon, although you may want to swap it out for a power sword or stiletto sword (this will require some converting if you want to use the coat). Other combinations that look good are twin sword champions, twin pistol characters (autopistol is probably the coolest but will need a conversion without the forgeworld kits), plasma pistol and sword or shock whip and either a pistol or another sword (this will need converting to remove the shock whip hand from the leaders coat). You'll want a few basic weapons, shotguns are pretty awesome (and have a new acid ammo option) and at least two lasgunners. I'd suggest raiding your bits box for any spare lasguns (or look online) which can then be given to
CC fighters as backup weapons and will give you tactical flexibility.
The options I went with can be seen in this thread:
https://yaktribe.games/community/threads/new-necromunda-painting-modelling-log.6296/
Hope that gives you some ideas.