I've been playing healers in MMOs since Dark Age of Camelot was a new game, and I can confirm that idiot DPS who don't work with the game mechanics (letting the tank get aggro, don't peel aggro off the healer when they are getting beat on, etc) are nothing new. The /ignore function is a lovely thing when using groupfinder. Add decent people to your friend list (/friend ) and /ignore the people who are annoying or don't know how to play. What /ignore does is keep Groupfinder from matching you up with people on your ignore list. It makes grouping a much more pleasant experience.
For leveling as a healer, I'd highly recommend finding a friend who plays at the same time you do, and level up together. It's how I leveled up my healing operative, and how I'm leveling up my healing scoundrel. It is a BLAST, and you get to see parts of class stories besides your own. Most people who play DPS or tanks would LOVE to have a reliable personal healer to level with. :)
As for which healing class - I really enjoy stealth as a healer, so I prefer operative/scoundrel. Being able to stealth allows you to skip fights you don't want when you are soloing. Also, in end-game progression operations, I find my healing operative is much more useful than my healing mercenary, because of the operative ability to heal while running, as well as her aoe heal. I'd say try playing the various heal-capable classes til 20, and then run with the one you prefer. It seems 2.0 will be addressing the healing weaknesses of each class at end-game.