So agree with thinking about how you will use the serger before you make a purchase. If you want to hem tee shirts (some of us are not 6 foot tall, and those overly long tee shirts look ridiculous on us!) you will need one with a cover stitch. Only a few sergers offer this. If you think you would use this feature a lot, you might buy a cover stitch machine -- and keep it set up just for this use.
Let's talk price -- if you are willing to learn the machine and to thread it yourself, you will save a bunch of money. If money is not an issue, the Baby lock self-threading machines are excellent - their self adjusting tension, and all the various functions are well worth the price... and there is a substantial difference in price -- only the top of the line offer the cover stitch. This is not a machine you would only want to use once or twice a year. If you have a local store which supports the Baby Lock line, you might want to see what serger classes they offer - using any serger! And there's a good class on Craftsy too -- often offered at a discount. I took it and learned alot.
PS: I do own a Husquvarna Viking S21. Learned to thread it myself with the computer disc tutorial. I use it in spurts -- 3-4 times a year for shortening things (it has the cover stitch), and am learning to sew tank tops and other knits items from scratch. The threading definitely had a learning curve. The only disappointment I've had with this machine is the tension adjustments are barely noticeable, but have managed to make it work for all my needs. My local LQS offers serger classes several times a year -- even using your serger to do quilts -- they can be quick and easy and very beautiful.