Well when it comes to quality comparisons with a cost savings I can say that dreamforge(I love my leviathans but damn I want one of those hover STUGGs) and dust tactics(the non pro painted ones you can get from vendors like miniature market) both have kits that easily rival GW.

As for mantic-With the exception of the tanks they are a bit lower quality when it comes to detail and options and not having instructions is also very annoying, but the fun of putting a squat army on the table at my FLGS makes up for it.