Welcome! I don't know anything about Berninas but I have had a Janome 6600 for 11 years and just replaced the thread cutter in January 2019. They are workhorse machines and you hardly ever hear of problems with them. You didn't say what kind of problems you are having with the 6600 but chances are it can be repaired.
Also a search of this forum will yield all kinds of discussions on machines.
Good luck with your choices.