I am a Superior Threads shopper. I get King Tut from Superior because the variegateds are really great color combinations. I also use So Fine quite a bit.
I also use Signature thread from another supplier once in a while.
I've not used serger thread in my longarm, so I can't give an opinion. I have tried a trilobal polyester thread which can be used in embroidery and had some tension issues with my longarm. I got the tension issues resolved, but then didn't like the way the thread looked on the quilt.