My experience is with sickle bar, we have used them for cutting hay forever.
None of my local dealers have used sickle bar mowersin stock, and the ones I've seen around for sale are junk. Dealers here also don't stock new ones. They aren't too anxious to order a new one, two of them said they had to buy them from the distributor in pairs, and they don't want one sitting around.
I saw drum mowers on CCM page, but don't know anyone who uses one or how they like them, or how long they last.
Disc mowers appear to be the most popular now, even with conditioners, but are more expensive.