I have learnt this much about domestic overlockers, if they try to do too much or are electronic, they tend not to do things all that well. My best is an old Bernina 800dl which is still an impeccable machine. I own a very big Elna that does many other things but its a big clunky thing that I don't like all that much. A 5 thread machine is only really used in low cost production so I would tend to go for a strong 4 thread machine that has manual thread tensions and importantly differential feed. Avoid anything electronic.
On my old Bernina I use #75 thread for the two needles and #120 for the two loopers, a lighter machine will have trouble with the heavier needle thread. If you can get a strong 4 thread machine, if you have a reason for a 3 thread variation you can just remove either needle to get either a wide or narrow overlock.