I have the Ovation, the latest and I love it. It does it all. It has 8 spool capabilities. It does not due the needle threading because with that many needles its impossible. Some of the older ones have the air and needle threader. I'd check Babylock's web site to see what each have. Mine is easy to thread including the needles because it has a little thing you can thread it with. It is easy to change from over lock to chain and you don't always have to change feet, it depends on what you do. Changing feet is easy, you just push a button to release old foot and put new one on, it takes like two seconds. I got a yr free of serger club and love it. I've done decorative stitches, made a heirloom night gown, a couple of different quilts, including a quilt as you go, a purse, lace, shadow stitching, and a couple of jackets and a gore skirt. I also have made a log cabin blanket with fleece, the serger keeps it from stretching. You can also quilt with it and you never run out of bobbin thread because there is none.
This being said, the newer sergers are easier to thread even without air. A month before I bought my Ovation I bought a Viking, 2nd to the top of line for them. Its easy to use and does it all. I only bought the Ovation because I love some of the features it has that none others have and I knew I could get my money back on my Viking. It was a store display model and the store wanted to get rid of it because the didn't have good luck selling sergers because they do mostly quilts. I knew it would be easy to get my 500 back considering it cost over 1300 and never been registered so it has a warranty. I just have to take time to list it. Try things out and see what you have in your area. In our area our sewing and vac sells Brother and Babylock and has great classes. Good luck