I have a Block Rockit and have great success with Omni thread. I tried a different brand and never could get the tension just right. I went back to Omni.....no more problems.
There are are two block Rockit groups that I know of. One on yahoo and one on Facebook. I have learned a lot there. Feel free to pm if you want to connect. I love my block Rockit and enjoy the fact that I don't have to worry about sandwiching my quilts!