Juki Serger Owners

I'm looking at purchasing a serger under $600(ish)

I've narrowed in on a few Juki sergers: 644d, 654de and 104d

Since I haven't touched a serger in 15 years, and only then briefly, I'm having a hard time figuring out what the differences are between these models and if the differences warrant the price differences.

If you have used any of the models I'd love to hear your experiences (especially in regard to noise level and ease of maintenance). If yours breaks what would you purchase next? If you had one in the past, what do you have now?

I plan to primarily make clothing with it, and unlikely to do any heavy materials (ie. Denim)

Thank you!!