I'm glad my machine isn't a thread snob- I just can't afford it.
The Bernina dealer tells me to only use things like Mettler- but so far it has sewn well with everything I've thrown at it.
I never buy the super cheap no name thread, but I have a HUGE amount of Dual Duty, and it sews that great. It also does really well with essential from Connecting Threads. And Isacord. Oh, and Mettler too.
I've also had no problems at all sewing with invisible thread (in both the bobbin and the top) and metallic thread (top only)