In my experience nothing beats time for proper aging of a juice. Time and a lot of hand shaking lead to juices aged to perfection. In my experience, heat steeping can lead to flavor fade and muting of some flavors. As far as cleaning, I treat my "vape dishes" the same as my kitchen dishes. They get a nice soak on hot, soapy Dawn water with a capful of bleach and a scalding hot water rinse. After that, I run mine through a baby bottle sterilizer and then air dry on baby bottle drying racks (saves counter space).
That being said, there are members who swear by crock pot steeping. On the low setting, the water will reach approximately 150 degrees. With the lid cocked and caps on glass bottles, with a periodic shake, this is said to speed the aging time. Some here use ultrasonic cleaners with heat. This heats and vibrates the bottles to speed the aging process.
There have been several different methods for speed-steeping and cleaning posted in the forum, from taping bottles to sawzalls to carrying juices in your pocket for a day, and also leaving them on the dash of a hot car, but in my personal experience, nothing tastes better than time.