I don't know much about the Janome however I know lots about the Viking machines, 1 have 3 of them.
The 140 has the sensor system where you select the type of fabric you are doing and the machine adjusts to the right pressure on the pressor foot so its just right for that fabric. It also has the auto lift pressor foot when it stops. This feature is so great with quilting because you set it with needle down and then when you stop the pressor foot raises so you can pivot without having to left the foot. There is no pressor foot lifter which some people have trouble doing, I love it so much!!!!!! It also has a 10 inch throat so there is plenty of room for free motion. Go and try this machine out, you won't be disappointed but see if you love the pressor foot lifter as much as I do. I will tell you that the auto pressor foot pressure feature is great. I never have rippled seams on different weight fabric like with my previous machines.
BE SURE TO TEST DRIVE each machine and see what you like. My one suggestion is to take some small pieces of your own fabric instead of using the "sample" fabric they use in the stores. It does make a difference. Finally, none of my 3 Vikings have ever been in the shop for repairs, just standard cleaning. I've had Vikings for over 20 years.