Before deciding on what serger you want, decide what features you need based on what kind of sewing you plan to do it. One of the biggest differences is whether it does a coverstitch (that double-needle hem at the bottom of t-shirts). A machine that does coverstitch as well as a variety of seam finishes is called a combo machine. Some people perfer to have a seperate coverstitch-only machine rather than a combo. Mine is a combo machine that does 3/4/5 threads.
I have a Bernina serger but they are made by Juki so I wouldn't hesitate to recommend a Juki serger. I hear that Babylock is considered a cadillac of sergers but I have never used one so I can't say. I did have a dealer show me the Babylock air threading and I am sure that makes it easier, but I've never really had any dificulty threading mine after I learned how. It takes a few minutes, and converting it to coverstitch (unthreading and re-threading an entirely different path) takes a few minutes, but I don't find it difficult, just time consuming.
Your best bet is to visit dealers and test sew the models that fit your price range. Have them show you how to thread since that is the part that a lot of people find difficult. If you don't have a local dealer, I am sure there are Ytube videos showing threading process. You might find a beter price from an online dealer (like Allbrands.com or Amazon) but check of a local dealer would have classes to help you learn to use it and make it more worthwhile to buy local.