there is a great little video on superior threads..all kinds of education videos..
http://www.superiorthreads.com/education/
I have had problems with certain threads, but it is usually a tension/needle issue.
i don't care for C&C because the spool got smaller and the price went up.
i use gutternman mostly but others too..
Connecting threads has great thread too..and not expensive either. you really need to look at the amount of thread on the spool and the price..Good threads are not that expensive when you looks at it that way.